You're in a good position mate, don't just buy the first one you get offered, buy the right gear and you won't have to spend twice!
Battery, buy one of these, 12V Battery for £20 and you'll find inside a 12V 17Ah battery, not difficult or anything to take apart, that is 1/3 of the price most places charge for the exact same battery.
Charger, buy one of these, Charger you'll never need another! These are the intelligent type that look after your batteries properly.
Lamp from here: NEF They say they'll price match, and it is the lad who runs this site, so you'll be safe ordering the