Battery technology: lithium cells, BMS and safe handling
What happens inside an electric bike battery, and why a damaged battery is dangerous
The battery is the part of the e-bike that sets it most apart from the classic bike — and the part that demands the most respect. As a mechanic you need to understand what's happening inside the battery cell, both to troubleshoot correctly and to work safely with it.
§How a working environment issue is handled
A lithium-ion cell consists broadly of a cathode (typically a lithium metal oxide) an anode (graphite on copper foil) a separator between them and an electrolyte with lithium salt ions. When the battery charges and discharges lithium ions move back and forth between anode and cathode through the electrolyte. An e-bike battery typically consists of many round cells (often called 18650 cells after their dimensions) connected in series and parallel to achieve the voltage and capacity the motor requires.
§BMS — the battery's watchdog
A BMS (battery management system) continuously monitors voltage current and temperature in each cell balances small differences between cells (cell balancing) and protects the battery from being overcharged discharged too far or overheated. If something goes wrong the BMS can shut the battery down or limit power before it becomes dangerous. A battery without a working BMS — or a BMS that has been bypassed — loses precisely that protection.
§Why damaged batteries are a special case
A battery that has been subjected to a blow a puncture or water can look completely normal on the outside even though the cells inside are damaged. So as a mechanic you must always treat a battery that has been in an accident severe heat or visible damage as potentially dangerous — even if it still charges and works. Store it separate from other batteries and flammable material and follow the workshop procedure for damaged battery cells.
- 01Always visually check the battery for dents, cracks and moisture damage before proceeding
- 02Only charge with the charger the manufacturer prescribes for that specific battery
- 03Avoid short-circuiting poles or puncturing the battery cell with tools.
- 04Store damaged batteries isolated and marked until they can be handled properly
§Transport and rules
Lithium batteries are dangerous goods under international ADR transport regulations and fall into class 9, the most restrictive tunnel category. A special provision (known as SP188) exempts smaller lithium-ion batteries from most of the heavy ADR requirements, such as requirements for ADR training and safety advisors, when batteries are transported in the normal way. But this relief does not apply unconditionally to damaged or defective batteries — you must assess and handle them according to a stricter standard because they simply do not behave 'normally'. Know your workshop's guidelines for when a battery should be sent for special handling.
§Reuse at end of life
When a battery is spent, it must be delivered to authorized collection and recycling—not in ordinary trash. In Denmark, the rules for producer responsibility and battery collection are gathered in the battery order, which is based on the EU's battery regulation and also covers the so-called LMT batteries (Light Means of Transport), which include e-bike and e-scooter batteries. The purpose is to ensure that valuable and partly environmentally damaging materials like lithium, cobalt, and nickel are recovered rather than ending up as waste.