The battery in my electric razor has failed to charge for several years. It does not turn on unless I leave it plugged in for 20 minutes and it turns off immediately if I unplug it. To save some money, save the world, and have some fun… I decided to take it apart instead of throwing it away.
Inside I found a black NiMH battery without much of a description. Is it safe to replace this with any old NiMH battery with any mAh capacity? The electric razor seems to work fine with the new battery… but charging it might be an issue if it is made specifically for the built in battery. The charger says the output is 15v DC at 420mA. Is there anything I should consider in replacing this battery?
I let the bad battery charge for an hour. It got up to 1.46 volts. After half an hour of letting it sit, its now at 1.39 volts.
I measured voltage of the batteries as they were attached and detached from the charger.
The good battery is charged to 1.41 volts and goes to 1.42 volts when attached.
The bad battery is charged at 1.39 volts and goes to 1.4 volts when attached.
I did something dangerous and discharged the bad battery with a paper clip. It's now at 1.21 volts and the voltage went to 1.33 while attached to the charger.
In any case, the voltage is in the right range for the new battery. I'm still not sure if its doing smart charging since it seems logical that the voltage difference will become less as it gets closer to the chargers voltage.
When I disconnect the battery and just measure the voltage across the battery connectors inside the razor, it measures .05 volts (while making a high pitched ringing noise). I'm guessing its doing some sort of smart charging if I haven't broken it yet.