A smart NIMH battery charger is more expensive than a dumb charger. So why should I get one?
First, with a smart charger you can just plug the batteries in and forget about it, come back later and it will be fully charged. With a dumb charger to be exact you have to compute the time needed. What if you computations are off? What if your computations assumed that the cell was flat when it had 10% charge?
With a dumb charger either you undercharge or overcharge a battery. An undercharged batt will of course not last as long. An overcharged batt will also degrade faster and not last as long. Yes, you can slowly damage a NIMH battery if you overcharge it. How much damage? Well, I dont know.