Ratshooter!!
+1 on what BHady said!
The lady at tower might have been trying to sell you a new charger, as the Nicad Wal wart charger would work with your NiMh cells, Heck, I have done it for years! But if you have a Hobbico charger, I would use that one, setting at a C/10 rate, I.E. 75 mAh and charge a minimum of 10 hours, wouldn't hurt to go 12 hours or so. if you do decide to charge at a 50 mAh rate, I would charge minimum 15 hours, preferably 17 hours or so! going a little longer, time wise, with a slow charge, such as what your are talking about, won't hurt your batteries but would ensure a full charge!
Craig.