Ours are charged by a mixture of engine,solar,generator + chargers and Aerogen, all of which have differing charge characteristics. If I had the space, I would be using golf cart or fork lift batteries. I've tried Enersol AGMs at over 300 euro each and found they lasted no longer than standard leisure at 100 euro. No prizes for guessing what I've replaced the Enersols with.
Even more puzzling than the domestic bank argument is - why do people spend crazy money on engine start batteries? Our unbranded car battery (on the boat) has now lasted for 7 years at a fraction of the cost.
Seems to me some people have the attitude that if it doesn't cost a bundle, it can't be any good and spend even more money on high tech charging methods for their overpriced batteries then spend more time watching the battery monitors than sailing.