Campervan leisure batteries: AGM vs lithium, sizing and real UK running costs

Your leisure battery is the quiet heart of a campervan. It runs the lights, the water pump, the fridge, the heater fan and the place you charge your phone. Get it right and you barely think about it. Get it wrong and you spend evenings rationing power, watching a dim control panel, and wondering why the fridge gave up overnight.

This guide explains the two battery types most people are choosing between today, AGM and lithium, in plain English. We will look at how each one behaves, how to work out the size you genuinely need, and what the real running cost works out at over the years you own the van. No jargon for its own sake, and no pretending one option is perfect for everyone. By the end you will know exactly what to buy and why.

What a leisure battery actually does

A campervan has two separate jobs for electricity, and most vans keep them apart. The starter battery under the bonnet exists to crank the engine. It delivers a big burst of power for a few seconds, then the alternator tops it straight back up. That is all it is built for.

The leisure battery, sometimes called a habitation battery, does the opposite. It sits in the living area and delivers a smaller amount of power steadily for hours: lights all evening, the fridge through the night, the water pump every time you wash up, the heater fan keeping you warm. It needs to be discharged slowly and deeply, then recharged, over and over, hundreds or thousands of times.

That difference matters because a starter battery hates being run flat, and a leisure battery is designed to cope with it. If you only remember one thing from this guide, remember that the right battery is the one built for the way it will be used. A leisure battery is a deep-cycle battery, and the question is simply which kind of deep-cycle chemistry suits you best.

The words you will keep meeting

• Amp hours (Ah): a rough measure of how much energy a battery holds. A 100Ah battery can in theory deliver 100 amps for one hour, or 5 amps for 20 hours.
• Usable capacity: the part of that you can actually take out without damaging the battery. This is where AGM and lithium differ hugely.
• Depth of discharge (DoD): how far down you run the battery before recharging. 50 percent DoD means you used half of it.
• Cycle life: how many charge and discharge cycles the battery survives before it noticeably weakens.
• State of charge (SoC): how full the battery is right now, shown as a percentage.

The two chemistries explained simply

There are a few battery types still sold for leisure use, but the real choice in 2026 is between AGM and lithium. The old flooded lead-acid battery, the kind you top up with distilled water, still exists at the budget end, but most campervan owners have moved on from it because it needs ventilation, regular maintenance and careful handling. We will mention it where it matters, but the main contest is AGM versus lithium.

AGM, the sealed lead-acid option

AGM stands for absorbent glass mat. It is a lead-acid battery, the same basic chemistry that has powered vehicles for a century, but the acid is held in a glass fibre mat rather than sloshing around as liquid. That makes it sealed, maintenance free and safe to mount in a living space without special ventilation. It will not spill if tipped, and it copes with vibration well.

AGM has been the standard leisure battery for years, and for good reason. It is affordable, widely available, easy to charge with almost any system, and forgiving of basic setups. It is the sensible default for someone who uses a van on weekends with hook-up.

Lithium, the LiFePO4 option

When people say lithium for campervans they almost always mean lithium iron phosphate, written LiFePO4 or sometimes just LFP. This is not the same chemistry as a laptop or phone battery. LiFePO4 is chosen for vehicles precisely because it is stable, slow to overheat, and built for thousands of cycles.

A LiFePO4 battery contains a small computer called a battery management system, or BMS. The BMS protects the cells from being overcharged, over discharged, run too hot or too cold, and drawn too hard. It is the reason a modern lithium battery is safe and reliable, and it is part of what you are paying for.

Lithium is more expensive to buy. In return it gives you far more usable energy per kilo, a far longer life, faster charging and steadier voltage. The rest of this guide is largely about whether those advantages are worth the price for the way you travel.

Usable capacity is where the gap opens up

This is the single most important idea in the whole article, so it deserves its own section.

A 100Ah battery does not give you 100Ah of usable power. How much you can actually take out depends on the chemistry.

With AGM, you should only routinely use about half the battery. Running a lead-acid battery below roughly 50 percent state of charge, again and again, shortens its life sharply. So a 100Ah AGM battery really gives you around 50Ah of comfortable daily use. You can dip lower occasionally, but make a habit of it and the battery ages fast.

With lithium, you can routinely use around 80 to 90 percent of the rated capacity with no harm. A 100Ah LiFePO4 battery gives you 80 to 90Ah of genuine daily use. The BMS will protect it before you do any damage.

So before you compare anything else, line them up honestly:

• 100Ah AGM gives roughly 50Ah usable
• 100Ah lithium gives roughly 85Ah usable

That means a single 100Ah lithium battery does the everyday work of nearly two 100Ah AGM batteries. When people say lithium is expensive, this is the first thing to factor in. You often need far less of it.

The headline number on the side of a battery is not the number that matters. Usable capacity is. Always compare what you can actually take out, not what the label claims it holds.

How each chemistry behaves in real life

Numbers only tell part of the story. The way a battery behaves day to day is what you will actually notice.

Voltage under load

As an AGM battery empties, its voltage sags. Lights dim a little, the water pump sounds tired, and devices that care about voltage can behave oddly. A lithium battery holds a steady voltage almost all the way down, then drops off near the end. In practice that means your kit runs at full strength right up to the point the battery is nearly empty. An inverter, for example, will deliver its rated power for far longer from lithium.

Charging speed

AGM accepts charge willingly when it is fairly empty, but as it fills it slows right down. The last 20 percent can take hours, because the battery refuses to take charge quickly without overheating. That is why a lead-acid battery left on hook-up overnight reaches full, but the same battery topped up by a short drive often does not.

Lithium accepts a high charge rate almost all the way to full. If your charging source can supply the current, a lithium battery refills dramatically faster. This is the difference that makes lithium so good for people who move every day and rely on the alternator or a short burst of solar.

Weight

Lithium is roughly half to a third the weight of lead-acid for the same usable energy. A 100Ah LiFePO4 battery weighs around 12 to 15kg. A 100Ah AGM weighs around 25 to 30kg. When you need a lot of capacity, the weight saving from lithium can be tens of kilos, and in a campervan every kilo counts towards your payload limit. We will come back to weight, because it can quietly become the deciding factor.

Temperature

Here AGM has one genuine advantage. Lead-acid happily accepts charge in the cold. LiFePO4 must not be charged below freezing, because charging a cold lithium cell damages it permanently. Good lithium batteries solve this with a built-in low-temperature cutoff in the BMS, and the better ones add a self-heating function that warms the cells before charging. If you tour in deep winter, this is something to check carefully rather than assume.

Discharging lithium in the cold is fine. It is only charging when frozen that is the problem. In a UK context, where a battery mounted inside an insulated van rarely drops below freezing even in January, this matters less than people fear, but it is worth knowing.

Self-discharge and storage

Both types lose a little charge when sitting unused, but lead-acid is worse and, crucially, it hates being stored partly empty. Leave an AGM battery flat over winter and it can sulphate and lose capacity for good. Lithium is happy stored at a partial charge and loses very little over months. For people who lay the van up from November to March, lithium is genuinely more relaxing to leave alone.

Cycle life and how long each one lasts

This is where the cost story really turns, so let us be specific.

A good quality AGM leisure battery, treated well and rarely taken below 50 percent, typically gives somewhere around 400 to 600 deep cycles. Treated roughly, run flat regularly, or left discharged over winter, it can be far fewer. In calendar terms, many owners get three to six years from an AGM battery depending on use.

A good quality LiFePO4 battery is usually rated for 2,000 to 5,000 cycles to 80 percent depth of discharge. That is not a typo. Even at the lower end, a lithium battery cycled once a day every single day would last several years, and most leisure batteries are not cycled every day. In normal leisure use, a lithium battery commonly outlives the van's other systems and can realistically serve ten years or more.

So the simple version is this: over the life of one lithium battery, you would likely buy two, three or even four AGM batteries. That single fact is the foundation of any honest cost comparison, and it is why a higher purchase price does not automatically mean a higher lifetime cost.

Working out the size you actually need

Buying a battery without doing this step is how people end up either short of power or paying for capacity they never use. The good news is the maths is simple. You add up what your kit draws, multiply by how long it runs, and you have your daily energy use in amp hours.

Step one, list your 12V devices and their draw

Everything in a campervan electrical system has a current draw, usually printed on it or findable online. Here are typical figures for common items at 12V. Yours will vary, so treat these as a starting point.

• LED ceiling lights: around 0.5 to 1 amp each
• Water pump: around 4 to 6 amps, but only while running, so a few minutes a day
• Compressor fridge: around 3 to 5 amps while the compressor runs, which is roughly a third of the time, so think 1 to 2 amps averaged over 24 hours
• Diesel or gas heater fan and electronics: around 1 amp running, more on startup
• Phone and tablet charging: around 1 to 2 amps per device while charging
• Laptop via inverter: around 5 to 8 amps at 12V depending on the machine
• USB and 12V sockets, small stuff: add a sensible allowance
• TV: around 2 to 4 amps

Step two, estimate hours of use per day

Now multiply each device by the hours it runs in a typical day. For example:

• Four LED lights at 0.75A for 4 hours in the evening = 12Ah
• Compressor fridge averaging 1.5A over 24 hours = 36Ah
• Water pump at 5A for 10 minutes total = under 1Ah
• Heater fan at 1A for 8 hours = 8Ah
• Phone charging, two devices, 1.5A each for 2 hours = 6Ah
• A bit of TV, 3A for 2 hours = 6Ah

Add those and you get roughly 69Ah per day. That fridge figure dominates, which is normal. The fridge is almost always the biggest single user in a modern van, so if you have a three-way absorption fridge running on gas instead of a compressor fridge running on electric, your daily figure drops dramatically.

Step three, decide how many days off-grid you want

If you always use hook-up, you barely need any reserve, because the charger keeps the battery topped up. If you want to spend two nights off-grid without recharging, you need two days of capacity. With our 69Ah daily example, two days is around 138Ah of usable energy.

Step four, convert usable into rated capacity

Now apply the usable rule from earlier.

• For AGM, divide your usable need by 0.5. To get 138Ah usable you need around 276Ah of rated AGM, so roughly three 100Ah batteries.
• For lithium, divide by about 0.85. To get 138Ah usable you need around 160Ah of rated lithium, so a single 200Ah battery, or two 100Ah, with comfortable headroom.

Look at that comparison. The same off-grid goal needs around 280Ah of AGM versus around 160Ah of lithium. The lithium bank is smaller in capacity, far smaller in weight, and you will not buy it again for a decade. This is the real shape of the decision.

A quick sizing shortcut

If you do not want to do the full sum, here is a rough guide for a couple in a typical campervan with a compressor fridge:

• Mostly hook-up, occasional night off-grid: 100Ah lithium or 2 x 100Ah AGM is plenty
• Regular weekends off-grid, no hook-up: 200Ah lithium or around 300Ah AGM
• Full-time or long off-grid trips with laptops and induction cooking: 300 to 400Ah lithium, paired with serious solar and alternator charging

Charging matters as much as the battery

A battery is only as good as the system that fills it. There are three ways to charge a leisure battery in a campervan, and the right battery choice depends partly on which ones you use.

Mains hook-up

When you plug into a campsite hook-up, a mains charger refills the battery. Older vans have a simple charger that suits lead-acid. If you switch to lithium, you usually need a charger that has a lithium charging profile, because lithium wants a different voltage curve. Many modern chargers have a lithium setting you simply select. Do not assume an old charger will charge lithium correctly. Check it, or budget to replace it.

Solar

Solar panels on the roof feed the battery through a solar charge controller, ideally an MPPT type which squeezes the most out of the panels. Solar and lithium are a fine match, because lithium accepts charge quickly, so even a short burst of strong sun puts useful energy back. With AGM, the slow acceptance near full means solar often cannot top the last portion in a single day. In the UK, solar is genuinely useful from spring to autumn and modest in deep winter, when short days and low sun limit output. Size your panels generously if you rely on them.

The alternator while driving

Driving charges the leisure battery through either a split-charge relay or, on modern vehicles, a battery-to-battery charger, often called a DC-to-DC charger. This is where lithium really shines. Because lithium accepts a high charge rate all the way up, an hour of driving can put a serious amount back in. A B2B charger rated at 30 to 50 amps can refill a lithium bank quickly between stops. With AGM, the battery throttles the charge as it fills, so the same drive returns less.

One important note for modern vehicles: many vans built in the last decade have a smart alternator that varies its output to save fuel. With these, a simple split-charge relay often will not charge the leisure battery properly, and a B2B charger is effectively required. If you are upgrading to lithium on a newer base vehicle, factor a B2B charger into your plan and your budget.

Switching to lithium is rarely just buying a battery. To get the benefit, you usually upgrade the charging too. Budget for the whole system, not the cell alone, and you will not be caught out.

The real UK running costs, worked through honestly

Now the part everyone wants. Let us put rough but realistic UK prices on each option and work out what it actually costs to own over time. Prices move, so treat these as representative 2026 figures rather than quotes, and always shop around.

Purchase price

• Quality 100Ah AGM: around £120 to £200
• Quality 100Ah LiFePO4: around £350 to £700, with self-heating and premium BMS models at the higher end
• Quality 200Ah LiFePO4: around £600 to £1,200

On the shelf, lithium clearly costs more. A 100Ah lithium can be three to four times the price of a 100Ah AGM. But remember two things from earlier: lithium gives nearly double the usable capacity, and it lasts several times as long. Both of those change the picture completely once you look beyond the first purchase.

Cost per usable amp hour

Let us compare on an equal footing using usable energy rather than rated.

• A £160 AGM giving 50Ah usable costs about £3.20 per usable Ah at purchase.
• A £500 lithium giving 85Ah usable costs about £5.90 per usable Ah at purchase.

So at the moment of buying, lithium is roughly twice the cost per usable amp hour. If you only ever do a handful of weekends a year on hook-up, and you plan to sell the van soon, AGM can genuinely be the cheaper sensible choice. There is no shame in that. The cheapest battery that does your job is the right battery.

Cost over the life of the battery

Now stretch the timeline to ten years, which is a realistic ownership window for many people.

Imagine you need around 85Ah usable, so either one 100Ah lithium or two 100Ah AGM.

• Lithium path: one battery at around £500, lasting the full ten years. Total roughly £500.
• AGM path: two batteries at around £160 each is £320 per set. If each set lasts four years, over ten years you buy roughly three sets. Total roughly £960, plus the labour and hassle of replacing them.

Over a decade, the lithium option in this example works out cheaper, not more expensive, even though it cost more on day one. That is the part the sticker price hides. The exact figures depend on how hard you cycle the batteries and how long your AGM survives, but the direction of travel is consistent: the longer you keep the van and the harder you use the power, the more lithium pays back.

Where AGM stays cheaper

To be fair to AGM, it remains the lower lifetime cost in several real situations:

• You keep the van only a few years before selling.
• You almost always use hook-up, so usable capacity matters less.
• Your power needs are modest and a single AGM comfortably covers them.
• You do not want to upgrade the charger and other parts that lithium often needs.

In other words, for a light user who plugs in most nights, AGM can be the honest, frugal answer. Do not let anyone make you feel you must spend on lithium if your use does not call for it.

The cost of charging the electricity itself

People often forget this, so let us cover it. The energy you put into the battery is not free, but it is small.

A typical UK campsite electric hook-up is included in the pitch fee or charged at a modest rate, often a few pounds a night or metered at a rate close to domestic electricity. Charging a leisure battery from empty to full uses only a kilowatt hour or two of energy, which at domestic rates of roughly 25p per kWh is well under a pound. Even charging daily for a fortnight, the electricity cost is a rounding error next to the pitch fees and the fuel.

Solar charging is free once the panels are paid for. Alternator charging uses a tiny amount of extra fuel, again negligible in the context of running the vehicle. So the running cost of a leisure battery is overwhelmingly about the battery itself, not the energy you feed it.

Total cost of ownership, the full table in words

Pulling the threads together, here is how to think about total cost over your ownership window:

1. Battery purchase: AGM cheaper up front, often by a factor of three or four.
2. Replacements over time: AGM needs replacing more often, which closes the gap and can reverse it past about five years.
3. Supporting kit: lithium may need a new mains charger, a B2B charger and sometimes a battery monitor, adding a few hundred pounds once.
4. Weight savings: lithium frees up payload, which has no pound figure but can be the difference between legal and overloaded.
5. Energy fed in: tiny either way, ignore it in the decision.
6. Hassle and reliability: lithium tends to be more set-and-forget, AGM needs more careful charging habits.

If your honest plan is short ownership and light use, AGM usually wins on money. If your plan is to keep the van for years and actually live in it off-grid, lithium usually wins on money once you account for replacements, and wins clearly on weight and convenience.

Weight and payload, the factor people forget

This deserves more than a passing mention because it catches people out. A campervan has a maximum legal weight, the gross vehicle weight, and the difference between that and the empty weight is your payload. Payload has to cover passengers, water, gas, food, bikes, awnings, and everything else you carry. On many factory campervans the payload is tighter than owners expect, sometimes only a few hundred kilos.

Batteries are heavy. If you decide you need a lot of off-grid capacity, the AGM route can add serious weight. Three 100Ah AGM batteries weigh roughly 80 to 90kg. The lithium equivalent that gives the same usable energy might weigh around 25 to 30kg. That 50kg or more difference can be the margin that keeps you under your legal limit with the family and the gear aboard.

If you are anywhere near your payload ceiling, weigh the van at a public weighbridge with everything loaded, and treat the battery decision as part of your weight management, not just your power budget. Being overweight is an MOT and insurance problem, not just a theoretical one.

Common mistakes to avoid

Over the years certain errors come up again and again. Knowing them in advance saves money and frustration.

Buying capacity you never use

It is tempting to fit a huge bank because more sounds better. But every amp hour costs money and weight. If you mostly use hook-up, a modest battery and a good charger beat a giant bank you never empty. Size for your real use, with a sensible margin, not for a fantasy of months in the wilderness.

Fitting lithium but keeping a lead-acid charger

If your charging sources still use a lead-acid profile, your lithium battery may never reach a proper full charge, or may be charged at the wrong voltage. You pay for lithium and get a fraction of the benefit. When you go lithium, check every charging source: mains charger, solar controller and B2B charger should all have a lithium setting or be lithium compatible.

Ignoring the smart alternator

On newer base vehicles, a simple split relay often will not charge a leisure battery properly because the alternator output varies. People fit a fresh battery, wonder why driving does not charge it, and blame the battery. The fix is a B2B charger sized to your needs. Find out what your vehicle has before you plan the system.

Running AGM flat repeatedly

The fastest way to kill an AGM battery is to run it down hard and leave it there. If you choose AGM, get into the habit of recharging before it drops below half, and never store it discharged. A battery monitor that shows real state of charge is worth fitting so you are not guessing.

Trusting the dashboard voltage alone

Voltage is a poor guide to how full a battery is, especially lithium, which holds steady voltage almost all the way down. A proper battery monitor that counts amps in and out, often called a shunt-based monitor, tells you the truth. For a lithium system in particular, a good monitor turns a guessing game into a clear number.

Mixing old and new batteries

When you have a bank of more than one battery, they should be the same type, age and ideally the same model. Pairing a tired old battery with a fresh one drags the new one down to the level of the old one. If you replace one in a bank, plan to replace the set.

Forgetting cold charging with lithium

If you genuinely camp in sub-zero conditions and charge the battery while it is below freezing, standard lithium can be damaged. Choose a self-heating lithium battery or mount it somewhere that stays above freezing inside the insulated living space. In most UK use this is manageable, but it should be a conscious decision rather than an oversight.

Safety, regulations and insurance

Leisure batteries are safe when installed properly, and both AGM and quality LiFePO4 are designed for use inside a living space. A few points are worth knowing.

AGM is sealed and does not need the dedicated ventilation that old flooded batteries required, but it should still be secured firmly so it cannot move in an accident, and the terminals must be protected against shorting. LiFePO4 with a reputable BMS is stable and includes multiple layers of protection, but the same rules apply: secure mounting, correct fusing close to the battery, and properly sized cable.

Fusing matters enormously. A leisure battery can deliver a huge current into a short circuit, enough to start a fire, so every system needs correctly rated fuses and the cable must be thick enough for the load. If you are not confident with this, have the installation done or checked by a competent auto electrician. A botched battery installation is one of the few things in a campervan that can genuinely be dangerous.

For insurance, a professionally installed and documented electrical upgrade is far easier to declare and prove than a mystery tangle of wiring. Keep receipts and, if you can, a simple wiring diagram. Some insurers want to know about significant modifications, so a quick call to confirm is sensible. None of this is onerous, but doing it tidily protects you if you ever need to claim.

Real-world scenarios to anchor the decision

Theory is useful, but let us put faces to it. Here are typical owners and what suits each.

The weekend hook-up couple

You head to a campsite most weekends, plug into the hook-up, and rarely camp without power. Your needs are lights, a fridge, charging phones and a bit of TV. A single 100Ah AGM, kept topped up by the hook-up, will serve you well for years at low cost. Lithium would work too, but you would not see much of its benefit, so AGM is the frugal, sensible choice here.

The off-grid weekenders

You like quiet spots without hook-up, two or three nights at a time, with a compressor fridge and the usual gadgets. You are the classic case where lithium starts to pay. A 100 to 200Ah lithium bank with a B2B charger and a couple of solar panels gives you genuine independence, fast recharging on the drive between spots, and a battery that will likely outlast your ownership. The higher price buys real freedom you will use.

The full-timers and long-trippers

You live in the van for long stretches, work from a laptop, perhaps cook on induction occasionally, and stay off-grid for days. Here lithium is almost the only sensible choice, paired with substantial solar and a strong B2B charger. The weight saving alone keeps you legal once you account for water, gear and the rest. A 300 to 400Ah lithium system is common at this level. The cost is real, but spread over years of daily use it is the lowest cost per day of power you can buy.

The occasional user who lays up over winter

You use the van a handful of times a year and park it for the winter. AGM can work, but you must keep it charged over the cold months or it will degrade. Lithium is more relaxing here because it stores happily at partial charge with little loss. If you hate the idea of trickle-charging through winter, lithium removes that chore, though for genuinely light use the lower AGM price may still win overall.

How to install or upgrade well

Whether you do it yourself or pay someone, a good battery setup follows the same principles.

• Mount it secure and accessible: firmly fixed so it cannot move, but reachable for checks and connections.
• Fuse close to the battery: a main fuse within a short distance of the positive terminal protects the whole system.
• Use correctly sized cable: thick enough for the current, with clean, tight terminals. Undersized cable wastes energy as heat and is a fire risk.
• Match the charging profile: set mains charger, solar controller and B2B charger to the correct chemistry.
• Fit a proper monitor: a shunt-based battery monitor tells you the true state of charge so you stop guessing.
• Keep it documented: note the battery type, capacity, install date and a simple wiring sketch for future you and for insurance.

If lithium tempts you but you have an older lead-acid system, you do not always have to replace everything at once. But be honest with yourself: a half-finished upgrade, lithium battery on a lead-acid charger, often disappoints. Plan the whole system, even if you fit it in stages, so each part works with the next.

What about LiFePO4 myths worth clearing up

Lithium has a reputation that is partly outdated, so let us deal with a few worries head on.

Is lithium a fire risk?

The dramatic fires you read about involve different lithium chemistries used in some consumer electronics and vehicles, not the LiFePO4 used in leisure batteries. LiFePO4 is specifically chosen for stability and is very hard to push into a dangerous state, especially with a proper BMS. Installed correctly and fused properly, it is a safe choice for a living space.

Does the BMS fail and brick the battery?

A quality battery from a reputable maker has a robust BMS and a meaningful warranty. Cheap, unbranded batteries are where reliability problems cluster. This is one area where buying a known brand genuinely matters. The BMS is doing important work, and a good one is worth paying for.

Will it really last ten years?

Cycle life depends on use, but the gap between lead-acid and LiFePO4 cycle life is so large that even pessimistic real-world figures still favour lithium heavily for anyone cycling the battery regularly. The main thing that shortens lithium life is abuse the BMS is there to prevent, so it tends to deliver on its promise far better than lead-acid does.

The bottom line

There is no single right answer, only the right answer for how you travel. Here is the honest summary.

Choose AGM if you mostly use hook-up, your power needs are modest, you keep the van only a few years, or you simply want the lowest price on the day and are happy to charge carefully and replace the battery sooner. It is a proven, affordable, sensible technology that still does a fine job for light users.

Choose lithium (LiFePO4) if you spend real time off-grid, you keep the van for the long term, you are tight on payload, or you want fast charging from the alternator and solar with a battery you can forget about for years. It costs more on day one, but for the way many people actually use a campervan it ends up cheaper per year, lighter, and far less hassle.

Do the sizing sum first, be honest about how you really travel rather than how you imagine you might, and remember that usable capacity and lifetime cost matter far more than the number on the label or the price on the shelf. Get those right and your leisure battery will do exactly what a good one should: keep the lights on, the fridge cold and your phone charged, while you get on with the reason you bought a campervan in the first place.