Battery charging - Charge alkaline batteries in manual andintelligent NiMH chargers

Manual chargers

It is known that alkaline batteries can be charged in manual chargers if you accept the risks, which most commonly is leaking if charged too long.

One method to circumvent the leak risk is to only charge for a few hours at a time and charge with the charger upside down with an absorbing bit of paper underneath.

Batteries that leak should be discarded.

Alkalines should be charged to 1.5-1.8 V at 100 mA or less, preferably in variating voltage - AC. Check periodically with a multimeter. The voltage will drop a bit after the charging has ended. Leaking can occur hours after so do not leave the batteries on delicate surfaces or in devices.

Intelligent chargers

Intelligent NiMH battery chargers often have protection circuits to detect and deny charging alkaline batteries. They also only charge to about 1.4 V because that is what NiMH batteries are rated for.

It is possible to circumvent the protection circuit by connecting alkalines in parallel. For example if the charger has slots that accepts 2 batteries in series then connect 2 additional batteries in parallel with these that also are in series.

The reason this works - I tried it on 2 chargers - is that NiMH has lower internal resistance than alkaline. The parallel batteries drops the resistance in the circuit enough to make it work. Note that I only tested for a couple of minutes so more prolonged tests are recommended.