When you get your new battery, don't let it sit below 12.3V~12.4V (no load voltage) for weeks. It will sulphate and reduce the effective capacity of the battery. Lead acid batteries don't like to be at below 50% state of charge.
My only 3 year old 110Ah Varta battery is struggling because the previous owner must have done just that, so it will charge 12.7V, but drops in minutes to 12.4, and after 4-5 days of no use goes down to 12.2. And I only have a parasitic drain of 0.2A ~0.3A
http://batteryuniversity.com/learn/a..._to_prevent_it
http://batteryuniversity.com/learn/a...tate_of_charge
http://www.batterystuff.com/kb/artic...ry-basics.html
Is a D3 solar roof wired to trickle charge the battery? if not that would be a excellent mod.