I set up a 'portable' studio for a shoot today using speedlight flashes hooked up with sync cables or slave units, and I noticed after a while that the recharge rates REALLY REALLY slowed down, but there was no way the batteries were flat from that amount of use. I changed the batteries in one unit mid session and noticed they were VERY hot - could this have been the reason?

Ive never used much in the way of the standard portable flashes in the smaller softboxes for shoots before, mainly just putting on the camera and intermittent use or proper studio lighting for more intense sessions.

So are speedlight style flashes just not up to more intense style studio sessions? Or am I doing it wrong?