you are going to need a voltage test meter to find the fault.but they can be bought for 5 to 6 quid,try somewhere like woolworths for one.charge the battery and put the black wire from test meter on the negative of battery . red on the positive side. voltage reading should be about 12.7 v. if it stays the same after say 3 mins ,the battery is ok. connect the earth wires to the battery,then connect each wire one at a time to the posative side. checking voltage reading each time.when you connect the circuit that is draining the battery ,the reading on the voltmeter will slowly start to drop. ie 12.6 12.5 12.4 ect. most of the ones ive tested turn out to be the alternator. hope that helps