How much mah does your battery have and at how many amps do you charge it?
Rule of thumb is not to charge your battery at a rate of more than one Amp per 1000 mah. Charging you battery more slowly will reduce the heat generated by the charging process.
Just as an example I use 9.6V 1600 mah batteries in my AKS-74U. I charge them at a rate of .9 mah and there is very little heat build up.