Batteries & Charging
Battery management system (BMS)
What is Battery management system (BMS)?
The electronics inside a battery pack that watch its cells and cut charging or power when temperature, current or charge level go outside safe limits.
A battery management system (BMS) is the electronics inside an e-bike battery that keep the cells within safe limits. Bosch says its system monitors the battery’s condition and protects against excessive operating temperatures, overload and deep discharge. The BMS also works out the state of charge you see on the display.
What it means for you
If a battery refuses to charge after a night in a cold garage, the BMS may be doing its job. Bring the battery indoors, let it warm to room temperature and try again with the original charger. Never try to bypass a BMS. If the battery still shows an error, take it to your dealer. Our winter battery storage guide covers charging after cold storage step by step.
Common confusion
A BMS doesn’t make every charger safe. The US Consumer Product Safety Commission warns against “universal” e-bike chargers, even when the plug fits. Use the charger that came with the bike or a replacement the maker approves. A BMS also can’t make a swollen or damaged battery safe to use.
Also known as: battery management systems
Related terms
- 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.
- 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.