Batteries can get warm or hot if they have a high internal resistance or the device using it have a high current consumption, "relatively" high to the battery.
considering its a photo cam, 3 things must be considered in my view: handling causes the device do warm up, due to skin heat transfer. second, the camera itself generate heat, that warm up the entire device itself. third, if you use flash, the camera technically need to pull a lot of power from the batteries in small amount of time, causing the high current consumption.
i believe you can do a test: use the same battery as usual, but don't hold the camera to not warm it up, and don't use flash. see if it gets hot. if still get hot, wold be nice to you test a battery that can give lot of amps (have low internal resistance) like eneloops.
also, the more important question, how "hot" is "your hot"? warm? lukewarm? burn your hand if you hold the batteries?
