Yeah, timed chargers aren't the best. They can under or overcharge your pack quite easily. Do your packs get warm at the end of the charge? If they are still cool, they are not charged all the way. If they are hot, they are being overcharged.
Do yourself (and your batts) a favor and get a decent peak detection charger like the one posted above. I've had great luck with a
MRC Superbrain 959 until I got my Hyperion charger, but the one posted above has slightly better features.