I have often suggested that folks read the "Ample Power Primer" (
www.amplepower.com, download from the tech tab and also find and download the wiring diagrams, too).
The Ample Power Primer
http://www.amplepower.com/primer/primer.pdfSorry, link is gone, Ample Power unfortunately closed. They were so ahead of their time! [May 2019]
The Ample Power Primer is still available on the Wayback Machine at
https://web.archive.org/web/20160323132827/http://amplepower.com/primer/primer.pdfIt remains one of the best...
Many thanks to Bill Murdoch
One often missed little gem in the Primer is a section entitled "Breaking In New Batteries."
http://www.amplepower.com/primer/break-in/index.htmlEssentially it recommends deliberately discharging new wet cell batteries to etch the plates and provide more surface area for the charge.
I didn't do it when we last bought a set of house bank batteries in 2006. Those batteries lasted just five years, partially because I did them an injustice by undercharging them over the years (see the "Gotcha Algorithm" topic:
http://c34.org/bbs/index.php/topic,4922.0.html) and leaving them disconnected for altogether too long when I had my skiing accident in early 2009 (not plugged in, solar panel not connected - I really did plan to connect it when I returned from that ski trip, but the hospital got in the way!

).
Two weeks ago we replaced those batteries with a brand new set of three 130 AH American Battery batteries. When I first used them on an overnight anchor-out trip last weekend, these "brand spankin' new" batteries wouldn't even run our fridge overnight! Holy cow, bad new batteries? NOPE. They just hadn't been broken in.
So I spent a few days earlier this week doing just that.
The result?
The fridge worked all night last night and is still going strong, the battery voltage remains high, and things work.
So, before you think your new batteries aren't working and there's something amiss with your electrical system or your fridge, break in those new batteries. They'll work better and last longer.
Always somethin' new...

This BTW, is VERY consistent with the "Old School" method of "just use 'em a few times and they'll work better" method. It's exactly the Same Thing, only under a controlled environment.