How Long Does It Take to Charge a Leisure Battery?

Whether you are topping up a campervan leisure battery or a cabin bank, knowing how long a charge will take helps you plan. The maths is simple once you know your charge current.

The formula

Charge time (hours) = Battery capacity (Ah) / Charge current (A), then add roughly 15 to 20 per cent for the absorption stage.

For example, a 100Ah battery charged at 20A: 100 / 20 = 5 hours, plus absorption gives about 6 hours from empty. In practice you rarely charge from fully flat, so real top-ups are quicker.

Charge current by source

Mains charger

Delivers a steady, known current, so it gives the most predictable charge time. A 20A mains charger on a 100Ah battery is the example above.

Solar

Charge current varies through the day with sunshine, panel size and your charge controller. Peak sun gives the fastest charging; cloud slows it right down. Size the array and controller for the current you need.

Alternator (DC-DC charger)

When driving, a DC-DC charger tops up the leisure battery from the vehicle alternator at its rated current, commonly 20A to 50A, giving a reliable charge on the move.

Safe charge rates: LiFePO4 vs lead-acid

Charge rate is expressed as a fraction of capacity, called the C-rate. LiFePO4 typically accepts up to 0.5C (50A for a 100Ah battery), so it charges quickly. Lead-acid prefers a gentler 0.1 to 0.2C and needs a longer absorption phase, so it effectively takes longer to reach full. Always follow the maker's figures.

Why the last part takes the longest

Batteries charge quickly through the bulk phase, then deliberately slow during absorption to top off the final capacity without overcharging. That is why the last 15 to 20 per cent takes proportionally longer, and why a quoted charge time is longer than the simple division suggests.

Work out your own charge time from any source with our free battery charge time calculator.

Frequently asked questions

How long does it take to charge a leisure battery?

Roughly the capacity in amp-hours divided by the charge current in amps, plus about 15 to 20 per cent for the final absorption stage where charging slows. A 100Ah battery charged at 20A takes around six to seven hours from flat.

What is a safe charge rate?

LiFePO4 batteries typically accept up to a 0.5C rate, which is 50A for a 100Ah battery, while lead-acid prefers a gentler 0.1 to 0.2C. Always follow the manufacturer's specification, as charging too fast shortens battery life.

Does the charge source change how long it takes?

Yes. A mains charger delivers a steady current, solar varies with sunshine and array size, and a DC-DC alternator charger is capped by its rating. Whichever you use, the charge current it supplies sets the time.

Do LiFePO4 and lead-acid charge differently?

Yes. LiFePO4 accepts higher currents and holds voltage well, so it charges faster and more fully. Lead-acid needs a longer, slower absorption phase to reach full charge and to avoid sulphation, so it effectively takes longer for the same capacity.