If the battery can no longer be charged, the cause is sometimes a so-called 'deep discharge'. This happens when the battery is sent into winter storage incorrectly, usually with too little charge, and/or is stored incorrectly. How this can be prevented can be found in the operating instructions or under BATTERY ‚Care: Mechanical / in operation / storage / safety'
Why is this happening?
Each individual cell in a Li-ion battery has a self-discharge, even if all consumers (including the BMS) are disconnected from it. This is known as calendar ageing. It results from the chemistry of the battery and cannot be stopped. In the event of a deep discharge, the voltage of the individual cells falls below 2.5 V and irreversible damage can occur in the cell.
You can find more details on this in my compendium on Li-ion batteries under AKKU - 'Theory & terminology compendium for Li-ion batteries' read more.
What can you do?
The following points can still be tried out on the Stromer battery without any safety risk before a new one becomes necessary.
- With a bit of luck, a battery will only 'appear' to be deeply discharged, but the cells are still alive and have a cell voltage above 2.5 V but below 3.2 V. Above this voltage, a Li-ion cell is considered empty (0% capacity). This threshold is relevant for most chargers. For safety reasons, they do not charge the battery if the voltage falls below 3.2 V.
The Stromer CR245 (& CR65) charger has a hidden ability. It can bring such a battery back to life if necessary. This is called 'recharging'. Simply connect the battery to the charger for 2-3 days and see what happens. With a bit of luck, the charger will start the regular charging process after a certain waiting time. The newer CR246 does not have this 'top-up' function but offers a 'floating charge'. - You can also send the battery to Stromer via the dealer. Stromer does not repair batteries, but can at least reset the self-protection and thus release the battery again. Here too, if the cells have really fallen below 2.5 V, Stromer will no longer release the battery.
- The last option is to replace the cells. However, the company in question must offer the option of resetting the SoH and charge cycle counter.
Further information can be found at AKKU - ‚Repair / Refit / Refurbishing / Occasions‚