Battery won't charge

When a battery won't charge, start with the charger, the outlet and the plug. They're the cheaper suspects and the easier ones to check.

Check first

1. Plug the charger straight into a wall outlet, and try another outlet. The Battery Network says to avoid power strips and extension cords (Battery Network rider guide), and Velotric suggests trying another outlet (Velotric troubleshooting).
2. Re-plug every connection and make sure each is fully seated, including the charger's adapter. Shimano's FAQ suggests this first (Shimano STEPS FAQ).
3. Read the charger light. Your manual says what each color means. On some chargers the light simply goes out when the battery is full, which Shimano says is normal (Shimano STEPS FAQ).
4. Make sure the charge port and plug are clean and dry (Velotric troubleshooting). Shimano's FAQ mentions cleaning its connection terminal with ethanol. Use your own maker's method.
5. Bring a hot or cold battery to room temperature first (Velotric troubleshooting). Bosch gives a charging range of 0 to 40 C (32 to 104 F) and says to let the battery cool after a ride (Bosch battery FAQ).
6. If the battery sat nearly empty for a long time, it may be in a protection state. Velotric says not to keep trying to charge it and to contact support (Velotric troubleshooting).

Never

• Don't open the battery case or the charger. Bosch says only trained personnel may open a battery housing (Bosch battery safety).
• Don't charge a battery that's swollen, cracked, hot or damaged (Velotric troubleshooting).
• Don't leave a battery charging overnight, while you sleep or while you're out (CPSC micromobility center).

Normal heat, and heat that isn't

Shimano says a battery or charger can get warm while charging, with surfaces above 60 C, and to pause and charge in intervals if that happens. A battery that is deformed, or stays hot after charging, is not normal and should go to your dealer (Shimano STEPS FAQ).

Next steps

If a known-good charger from the same maker charges the battery, you only need a new charger. If you lost yours, CPSC says to ask the bike's maker for a compatible replacement (CPSC charger warning). If no charger works, the pack needs a test. Shimano notes a battery that won't take a charge may have reached the end of its service life (Shimano STEPS FAQ). Some packs, like Rad's external ones, also have a fuse, which is a job for a shop or the maker's support (Rad no-power guide). If the pack is worn out and the maker no longer sells a replacement, see battery rebuilders and replacement pack builders. See battery care.

Sources

• E-bike battery safety, a guide for riders, The Battery Network
• Electric bike troubleshooting guide, Velotric
• Shimano STEPS FAQ, Shimano
• 12 questions about your eBike battery, Bosch eBike Systems
• Warning on universal chargers, CPSC
• Battery handling and safety, Bosch eBike Systems
• Micromobility information center, CPSC
• Troubleshoot a bike that won't turn on (external battery), Rad Power Bikes

Stuck after these checks? Find a shop near you.