Hi Paul
I have a 110 amp leisure battery paid £48 two years ago, this will stay up for a week without a charge, but a split charge relay from a local man cost me a £5 pluss £25 to fit it.
But be carefull get a sealed maintance free one as I had one that was not and acid would trickle out, and they have to be vented properly. But you dont have that trouble with the maintance free ones.
roy