Your batteries are the "hot" part of this deal - as in the charger charges 'em way too quick, drastically shortening battery life. Out of probably 40-50 new/almost new AA's & AAA's I've charged, 2 have vented (not Rayovac; nevertheless, good quality cells). After the first 20 batteries or so, I started running a 12" Patton commercial-industrial fan to cool the works; batteries don't get very warm but there's just too much chemical reaction taking place in too small an enclosure over too little time. IMHO, it'd be better to spend $40-60 on a slower charger that peaks each individual cell.
No animals were harmed in the testing of this product was developed, but a couple of engineers should've been taken out behind the barn and shot.