Which is more important volt or current regulator

Hello
I would like to know which is more important to have a voltage or current regulator.
I have a solar cell that put out 12 volt with around 5 watts output with no load.
I want to use the solar cell to charge Nickel metal hydride battery 1.2 volt.
Want to charge maybe one battery or maybe more than one at different time.
Is there a circuit somewhere that automatic disconnect the solar cell from the battery once the battery is fully charge by the solar cell ?
Thank for the help,mrel

For charging NiMH batteries you should have a current regulator. A voltage regulator would cause high charging currents.

Unfortunately there's no easy way to tell when a NiMH battery is fully charged. Thus if you want to charge the battery at higher than it's trickle charge rate, you need a special circuit to determine when the battery is charged. This may involve a temperature sensor that detects when the battery is heating up, which indicates it's charged. Companies such a Linear Technology and TI sell ICs just for charging batteries.

A homemade charger that you could perhaps adapt to your needs is at NiCd Battery Charger.