Let’s make sure: NiMH batteries can be charged in series, but the correct method should be used.
In order to charge NiMH batteries in series, the following two conditions must be met:
1. The nickel metal hydride batteries connected in series should have a corresponding matching battery charging and discharging protection board. The role of the battery protection board is to manage multiple electric cells to achieve more efficient charging and discharging effects. It can intelligently coordinate the current size of many electric cells during charging and discharging as consistent as possible, This also ensures that the battery will be charged in series with excessive differential pressure (because the internal resistance difference or differential pressure is too large, the battery with small capacity and voltage will be charged first, and the battery with large capacity and voltage will continue to be charged), which will lead to overcharge, affect the battery life or cause accidents.

2. The charging parameters of the charger should match them
After the nickel oxygen battery is connected in series, the voltage will increase. In this case, the charger needs to change to a higher voltage. Of course, the voltage value should match the size of the battery connected in series. Of course, another important point is that the charger’s ability to coordinate charging should also be enhanced, because the stability of the battery pack will decline after the number of cells increases, and it becomes more difficult to achieve coordinated charging of multiple cells.

The above is the reason why NiMH battery can be charged in series, but there must be a corresponding charging method.