If you want to prevent the cells from getting hot during charging, use a charger with a lower mAh rating.
I have several (OK, about a dozen ) airsoft gun batteries here, and with the charger I use I have the option of a slow or fast charge. The fast charge dumps about 1.5 amps in to the cells, and although they charge in about a tenth of the time a slow charge would take, the battery does get exceedingly hot! The slow charge uses a 130mAh trickle feed, which can take up to 48 hours to fully charge a battery, but they'll barely get warm.
If you're not going to be using a 'smart' charger that cuts off automatically, remember the formula for charging times for empty cells...
(mAh rating of battery / mAh rating of charger) x 1.4
Also make sure you're using NiMH batteries as these don't develop a memory. To be on the safe side when charging, it's good practice to run the cells down completely (I use an 80mm PC fan as a discharger) before recharging them.
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