My glow plug igniter has a 3000 Ni-HM in it and I leave it plugged in between races (Fri to Fri) with no problem! It came with a Ni-CD that went bad so I put the Ni-HM in.
BUT I'm not charging a 6 cell am I!!!!
I have use this charger to charge one cell at a time (a 6 cell pack) to find the bad cell.