Please invest in a good, e.g., La Crosse or Maha, charger if you're serious about NiMH rechargeables. At some point, one battery will begin to fail. If you don't know which one, you'll have to toss all four. Bad idea.
The better (and more expensive) chargers will charge, thoroughly test, and display data upon each battery individually. They'll also give you the ability to deep discharge and condition batteries as a group or one at a time.
You'll never wonder about battery status again - meaning you'll sleep better, have better digestion, and experience less hair loss.