How to make your backup batteries last longer

Last checked 9 November 2026

Batteries are usually the most expensive part of a backup system to replace. How you use and keep them can make the difference between a battery that lasts many years and one that disappoints within a few seasons.

For every type of battery

Keep them cool. Heat is the biggest enemy of battery life. Install batteries in a shaded, ventilated spot: never in direct sun, a hot roof space or a closed cupboard next to the inverter.
Don’t drain them flat. Use the depth of discharge your battery was designed for: about 50% for lead-acid, and the maker’s figure (often about 80%) for lithium. Set the inverter’s low-battery cut-off to match.
Recharge promptly. Don’t leave batteries sitting part-empty for days.
Keep connections clean and tight. Loose or corroded terminals waste energy and get hot. Switch off and isolate the system before touching any connection, or have your installer check them.
Use matching batteries. Same type, capacity, brand and age in a bank. Adding one new battery to an old bank shortens the life of the new one.
Make sure the charging settings match the chemistry. Inverters and charge controllers have profiles for lithium, AGM, gel and flooded batteries. The wrong one can overcharge or undercharge them.

Lead-acid: flooded, tubular, AGM and gel

Full charges matter. Lead-acid batteries left partly charged build up sulphate on their plates, which permanently reduces capacity. Make sure they reach a full charge regularly, from solar, the grid or a generator.
Top up flooded batteries with distilled water only, to the level the maker recommends, after charging rather than before. Never let the plates become exposed.
Ventilate. Flooded lead-acid batteries give off hydrogen when charging. Keep them in a ventilated space, away from sparks and flames.
Equalising: some flooded batteries benefit from an occasional controlled overcharge to balance the cells. Only do this if the manufacturer recommends it, and as they describe. Never equalise AGM or gel batteries unless the maker says to.

Lithium (LiFePO4)

Let the battery management system (BMS) do its job. It protects the cells from overcharging, deep discharge and extreme temperatures. Don’t bypass it.
Charging in the cold: most LiFePO4 batteries must not be charged below about 0 °C (32 °F). Many block charging automatically; some have heaters.
Partial charging is fine. Unlike lead-acid, lithium doesn’t need to reach 100% regularly.
Long storage: if the system will be unused for months, the usual advice is to store lithium batteries part-charged, often around half full, and switched off. Check your maker’s guidance.

Signs a battery bank is wearing out

noticeably shorter runtime than when it was new, at the same load
the inverter’s low-battery alarm going off soon after an outage starts
batteries getting hot while charging
swelling, leaks or a smell of rotten eggs from lead-acid batteries: switch off and get them checked

When it is time to replace, compare options on cost per usable kWh over their life, as explained in lithium vs lead-acid, and re-check your sizing in the calculator.