3&1/2 minutes is way too long, the cell has boiled inside and the electrolyte has leaked out. That electrolyte is corrosive, so clean out the chassis tub on your car or the battery contacts will corrode and stop conducting.
A simple way to to use a 3v power supply to charge BCGs is to use a series load resistor. A 2 ohm 5 watt resistor in series with the positive wire that is connected to the battery will trim down the initial charging voltage and make the charging current a little more constant throughout the charging period.
I would guess not more than 2 minutes, but when you first charge this way, monitor the cell temperature, once you have a noticible MINOR rise in temp, then thats enough. Check the charging time (in seconds), and use this time for charging from then on.
Its not the scientific way to charge a NiCd or NiMh, but it will do. Those litle cells are pretty robust, although once they leak the are on a quick path to death.
:)uA
