Is a bigger leisure battery always better?

No. A pack much bigger than you need costs more, weighs more and rarely gets cycled. Size it to your real daily use plus a buffer, not the biggest number that fits.

Do I need to account for solar when sizing a battery?

If you have solar or charge while driving, you can run a smaller battery because it is topped up through the day. Estimate your solar yield first, then size the battery around the shortfall.

How should I charge a leisure battery while driving?

Through a DC-DC charger (battery-to-battery), such as a Victron Orion, which is what we recommend for a clean, controlled charge that also protects the starter battery. A split-charge relay works but is less reliable for lithium and some relays cause a backfeed that skims around the top 15% off usable capacity. Feeding straight off the alternator with no relay and no DC-DC is not recommended.

Battery sizing

What size leisure battery do I actually need?

Q: How is lithium different to size than lead-acid?

With lithium you can use close to 100 percent of the rated capacity, so you buy the number you need. Lead-acid should only be taken to about half, so you would need roughly double the rated capacity for the same usable energy.

Most people either buy too small and run flat by morning, or massively over-spend on capacity they never use. Sizing a battery is not guesswork. Work out how much power you use in a day, decide how long you want between charges, and the number falls out of the maths. Here is how to do it in a few minutes.

Size my battery now→ See the TITAN range→

The method in three steps

This is the same logic our calculator uses. Do it on paper if you like, or let the tool add it up for you.

STEP 1

Add up your daily use

List everything you run, its power draw in amps, and how many hours a day it is on. Multiply and total it. That gives you amp hours used per day. A fridge, lights and charging is usually 40 to 60Ah a day.

STEP 2

Decide your days between charges

How long do you want to last with no hook-up, solar or driving? One night is very different to a long weekend. Multiply your daily use by the number of days you want to be self-sufficient.

STEP 3

Match it to a lithium pack

With TITAN lithium you can use the full rated capacity, so the number you worked out is the number you buy. With old lead-acid you would need roughly double, because you can only safely use about half.

Typical setups and the size that fits

A quick starting point based on how people actually use their vehicles. If you run an inverter for cooking, size up.

Your setup	Roughly per day	Good fit
Weekend campervanFridge, lights, phone and laptop charging	40 to 60Ah	100Ah to 120Ah
Touring motorhomeAdd diesel heater, water pump, TV, a few days off-grid	60 to 90Ah	150Ah to 180Ah
Full-time or inverter cookingInduction, microwave, coffee machine, longer off-grid	100 to 180Ah	230Ah+
Boat or off-grid house bankMultiple days, heavy loads, sustained inverter use	180Ah+	280Ah to 460Ah

These are starting points, not a substitute for adding up your own loads. Two minutes in the battery size calculator gives you a number tailored to your kit.

What uses what

Rough daily draw for common items, so you can sanity-check your own total.

Appliance	Power	Typical per day
12V compressor fridge	40 W	20 to 40Ah
LED lighting	12 W	3 to 8Ah
Diesel night heater	18 W	5 to 15Ah
Water pump	60 W	2 to 5Ah
Laptop and phone charging	60 W	5 to 12Ah
TV or projector	45 W	5 to 10Ah
Kettle or induction (via inverter)	1800 to 2000 W	10 to 30Ah per use

Solar and the alternator change the answer

Everything above assumes no top-up. In reality, most vans charge while driving and many carry solar, both of which put energy back during the day. If you have a decent panel, you can run a smaller battery than your raw daily use suggests, because the pack is being refilled as you go.

A single 100W panel puts back around 25Ah a day on average between April and October in the UK. Add that to your charging on the move and the battery rarely starts a day empty. To see how panels change your numbers, use the solar calculator, then come back and size the battery around the shortfall.

Work out my exact size→ Estimate my solar→

Common questions

What size leisure battery do I need for a campervan?

For a typical campervan running a fridge, lights and charging, 100Ah to 120Ah of lithium covers a long weekend off-grid. Add a diesel heater, water and a TV and most people are happiest with 150Ah to 180Ah. The honest answer depends on your daily use, which you can total in the battery size calculator.

Is a bigger battery always better?

No. A pack that is far bigger than you need costs more, weighs more and rarely gets cycled, which wastes both money and payload. Size it to your real use plus a sensible buffer for bad-weather days, not to the biggest number you can fit.

How is lithium different to size than lead-acid?

With lithium you can use close to 100% of the rated capacity, so you buy the number you actually need. Lead-acid should only be taken to about half, so you would need roughly double the rated capacity to get the same usable energy, at far more weight.

Can I add a second battery later?

Yes. TITAN packs can be wired in parallel to grow the bank as your needs change. It is often cheaper to start with the right single battery, but parallel is a valid path if you expect to scale up.

Do I need to account for solar?

If you have solar or charge while driving, you can run a smaller battery, because it is topped up through the day. Work out your likely solar with the solar calculator, then size the battery around what is left over.

How should I charge the battery while driving?

Through a DC-DC charger, also called a battery-to-battery charger, which is what we recommend. We would fit a Victron Orion every time for a clean, controlled charge that also protects the starter battery. A standard split-charge relay does work, and many vans already have one, but it is not the most reliable way to charge lithium and some relays cause a backfeed that quietly skims around the top 15% off your usable capacity. Feeding straight off the alternator with no relay and no DC-DC is not something we recommend.