I am trying to charge a 7.2v 1600mAh nickel medal hidride 5 cell battery pack and i'm using a variable switch which can take the power supply down to exactly 7.2volts. i have been told that the power supply produces 1 amp and the battery is only 1600mAh.
I'm not quite sure how to stop the battery from over charging, is there a little relay or something that will do it?
A nickel metal hydride cell is pretty delicate when it comes to charging. You can't just hook it up to a power supply and let it charge. The charge must be controlled by a circuit that can sense when the battery is approaching capacity and shut off the current.
The battery will overheat quickly past 100% charge, and the pressure inside will spike steeply, causing the casing to rupture or explode.
These types of batteries like a three-stage charging scheme. A fast charge rate gets it to 80 or 90% charge. A timed charge tops it off, then a trickle charge "floats" the battery. This is a pretty complicated circuit, and will requires some form of IC control. I suggest you find out who manufactures the battery and contact them to obtain a proper charger.
Wiring the battery to the power supply will drastically shorten its life unless you carefully control the charging time.