Start battery + domestic battery

Hey geeks,
SO my 2007 Defender puma has the original battery and its dying. I need a new one, and while in there I want to put a domestic battery & split charger so I can run a night heater and charge my various electrics while camping.

Anyone got advice on a smaller but equally as powerful start battery & experience in the domestic one?

Any advice - apart from some massively expensive exotic batteries that will cost me £400 thank you!

I would use a caravan leisure battery for your second battery as they are designed to be deep cycled many times without adverse effect, and a normal heavy duty battery for your starter battery.