How to store and maintain batteries the right way

What state of charge is right for storage?

For storing lithium-ion batteries a state of charge of 40 to 60 % is ideal. A fully charged cell sits at high voltage and ages faster, while an empty cell risks slipping into deep discharge through self-discharge.

At around 50 % charge the chemical stress on the cell is lowest, so usable capacity is largely preserved over months. Lead-acid batteries are the exception: they are stored full and topped up regularly, because a deep discharge immediately causes sulfation.

• Lithium-ion / Li-polymer: charge to 40‑60 %, neither full nor empty.
• LiFePO4: 50 % is enough, very low self-discharge.
• Lead / AGM / gel: charge fully and top up regularly.
• NiMH: about 40 % charge, store cool and dry.

How do temperature and humidity affect a battery?

Storage temperature is the second major lever against capacity loss. Cool 10 to 15 °C in a dry environment is ideal. The warmer the battery, the faster the chemical ageing processes run.

At 25 °C a lithium-ion cell loses noticeably more capacity per year than at 15 °C, and at 40 °C the loss accelerates sharply again. Frost below 0 °C barely harms storage itself, but a cold battery must never be charged, because metallic lithium would otherwise plate out.

How often does a stored battery need topping up?

Every battery self-discharges, even with no load connected. A stored battery therefore needs a fixed top-up interval. Check lithium-ion every 6 to 12 months and, if needed, recharge back to 50 %.

The biggest danger is deep discharge: if cell voltage stays below roughly 2.5 V, the cell can be permanently damaged and recharging becomes hazardous. Lead-acid batteries need a tighter interval of about 3 months, otherwise sulfation lowers capacity for good.

• Lithium-ion: check every 6‑12 months, recharge to 50 %.
• Lead / AGM: top up fully every 3 months or use a float charger.
• Never let voltage fall below the cell's discharge cut-off.
• Do not recharge deeply discharged Li-ion - recycle it properly.
• Use an automatic maintenance charger instead of constant current.

Frequently asked questions