Batteries & Charging
Self-discharge
What is a Self-discharge?
The slow loss of charge inside a battery while it sits unused, caused by chemical reactions in the cells.
Self-discharge is the charge a battery loses on its own, with nothing plugged in and the bike switched off. It comes from slow chemical reactions inside the cells. Tern’s Bosch battery guide puts it plainly: batteries self-discharge over time even when not in use.
Why it matters over winter
Lithium-ion e-bike batteries lose charge slowly. Bosch describes them as having low self-discharge. But over a long winter, a pack stored low can still drift toward empty, and Switzerland’s fire-prevention service BFB warns that recharging a deeply drained battery carries extra fire risk. That’s why battery makers set a storage charge and a check schedule. Shimano, for example, says to recharge its STEPS batteries every 6 months.
Common confusion
Self-discharge is different from standby drain, where electronics on the bike draw a small current while the battery stays fitted. Both lower the state of charge. Neither means the battery has lost capacity for good, which would show up in its state of health. Our winter battery storage guide explains how often to check a stored battery.
Also known as: self discharge
Related terms
- State of charge How full a battery is right now, shown as a percentage or as bars on the display. It is an estimate made by the battery's electronics.
- State of health How much of its original capacity a battery has kept, usually given as a percentage of what it held when new.
- Lithium-ion battery A rechargeable battery that stores energy by moving lithium ions between two electrodes. Almost every e-bike battery is a pack of lithium-ion cells.