if you want more/ back up power, you may be able to consider a twin battery set up with split charging? not got it myself but i know its favoured by the winchers out there. you will have to move some parts around on the opposite side of the rad, but i believe it possible to fit another battery in there. i think it was even a factory option on early RRC? though not on later models?
personally i think you can't really go wrong with Bosch. i have one on my RR and its been brilliant for the past 7yrs and still going. only once had a problem when the interior light was left on for a few days. but i charged it up again on the mains, without an issue. 12v batteries don't like to being fully discharged and it can damage them apparently, but if you can charge it on the mains sometimes you can rescue them back to life.
again had the same thing on my jag, with a Varta battery, but a few goes with mains charger brought it back without a problem.
the way i buy batteries is to measure the available space in the battery tray, go to the shop with the measurements, and buy the largest physical size you can fit in. take your tape measure!
i think whatever brand you choose its worth going for one with atleast a 3 yr warranty, but better ones offer 4 or 5yrs.
other good brands are Varta, Yuasa, AC Delco. i wouldn't bother with cheapo no brand chinese stuff!
i think something around 72Ah is adequate for normal use myself. expect to pay £80- £90 region for a good one.
1990 RRC Vogue SE 3.9 V8 LPG, usual off road mods
Jaguar XJ40 x6!