the gun you are using will sort of dictate what battery you require
if you have a crane stock - the MOST LIKELY the battery will be in there
(not always the case - some guns with crane can still have battery at front handguard)
if you have crane - AND BATTERY IS IN THERE then nunchuck is what you require
nunchuk types can be used in many guns - even front handguard ones usually
unless you buy something like MP5 or FireHawk that may require a stick battery
Raider will have crane and battery at back I think - stock is low on many sites coz they got rails
Carbine - no rails and battery up at front - in stock at many places and a tiny bit cheaper
battery on carbine is at front hanguard - well in general unless spec has changed
nunchuk you looking at is a 3 + 1 + 3 - the one in centre - hmmmm
maybe a 4 + 3 layout will be better I would tend to think & should fit up front/back whatever
or 4+4 = 9.6v but this is getting a bit on the powerful side and if you really have room
component shop or ebay - or component shop on ebay - should get a battery + smart charger
for £15 + £10 = £25 - smart charger would stop your normal nimh cooking with cheapo charger
(smart chargers should stop charging when complete - but always keep an eye when charging batteries)
Lipo is another option but different charger or a more deluxe one that does all types - but as always you
need to check if batteries YOU buy will fit/work with YOUR gun.....
I mean if you are that pushed and got a battery that don't fit/too big you can get by by taping it on side of
stock/receiver, many do this to get them out the crap when needed
guessing is not good idea - measure if unsure, digital vernier/caliper guage for about £4 is a real help when
buying extra batteries that may/may not fit.....
blimey - mega waffle about batteries and you ain't even bought gun yet - soz for going on