You want to get a 'smart' charger, and avoid the quick chargers. Fast charging generates a lot of heat, which shortens the number of recharge cycles you get. Smart chargers will stop the charge when their done, so you can leave them and not worry about overcharging. NiCd and NiMH are both 1.2 volts. The thing about Eneloops, is that the have a low self-discharge, won't go dead sitting unused. Not a huge deal with metal detecting, you usually plan ahead enough to charge up before hand.
Found some rechargeable alkaline batteries, 8 AA's and a charger for $16 early this year. Been working well, no leaks, no issues, last a lot longer than NiMh. Haven't had any leaks or failures from the batteries that came with the charger, but have had some Duracels leak after 5 recharges... The charger is great, it's a smart charger, does both Alkaline, and NiMH, and no heat, not even a little warm. The Company is IGO Green, Canada, I think. The charger is worth $16 by itself.
