Don't worry about hoppers electronics, they'll be fine.
ni-cad's (nickel cadmium) only produce 8.4v at about 110mAH whearas a normal battrey
gives 9v at about 200mAH. if your thinking of getting re-chargables get ni-mh (nickel metal hydride)
, they have the same voltage as ni-cad's but a higher current rating (150mAH) and will power your hopper longer.
they CANNOT destroy your hopper cos it will only take the amount of current it needs from the battries, it's the voltage that's important.
if you get ni-mh battries you will have to get a ni-mh charger, they charge different to ni-cad's
as for cost effectiveness, i've been playing 12 years and have always used rechargables, so far i've had to buy 6 @ £5 each,
if your replacing your battries each time you play do some sums and you'll probably come to the same conclusion i did.