HP-41 Batteries

[Dieter]

(11-30-2014 01:44 PM)Joe Horn Wrote:  Any "smart" recharger works fine, using magnets to provide contact.

I agree that an intelligent charger is mandatory since it works fast and protects the batteries against overcharge and other problems. On the other hand not "any smart recharger" can be recommended. Assuming a typical NiMH N-size cell capacity of 400-500 mAh and a limit of 0.5 CA, the charging current should not exceed 200 mA, preferably 150 mA. Most intelligent chargers are designed for AA and AAA batteries with much higher capacity and thus they provide much higher charging currents. Some better chargers can be set to suitable lower currents, e.g. the well-know BC700 with a default setting of 200 mA. So an empty 400 mAh N-cell will be charged in about 2.5 hours.

Regarding the other option of replacing the old cells in a HP 82120A battery pack with current NiMHs, using the original HP charger (82066A, 82059A etc.): I asked my local battery supplier and ordererd a custom made pack of four 1/3 AAA (or 1/2 N) cells, professionally welded and ready to be used in the original (empty) battery pack. Most battery refurbishment/rebuilding services should be able to do this.

However, using regular N-size NiMHs in a standard HP41 battery holder and charging these in a decent processor controlled external charger technically is the better option. It provides much more capacity, decent charge control – and it requires no soldering or other inconveniences. ;-)

Dieter