battery woes

Mickpaj.
Your battery is probably OK, very few people understand battery testing. If you get a charger on it for a few hours and then measure the voltage, with the charger off, you may save it. When a battery has been flat for a long time the plates get a white coating on them, this takes awhile to dissolve as you charge it, so you may have to charge it for many more hours. Eric

I find it strange that you have a stuffed deep cycle battery that is less then 12 months old. Even if you fully discharged it every time you used it you should get at least 300 cycles out of it before it will loose capacity provided you have fully recharged it every cycle.. The proper way to charge a deep cycle battery is SLOWLY over a long period at low amperage (less than 10amps . If fully discharged this can take 3 or more days depending on the capacity. A deep cycle battery is not designed to take fast charges at high amps like normal start batteries which are used to delivery high current for short period whereas a deep cycle battery is designed to delivery low current over long period.
From experience I have found to get the best performance & long life out of a deep cycle battery is to never discharge it more than 50% (ideal is not below 75%). On an average I can get from six to eight years out of a deep cycle battery using this method. I have spoken on this topic many times on this forum over the years & I have the batteries to back it up. Cheers.

Mickpaj - More info please. Have you left it for any length of maintenance charge? Have you left it flat for more than 12 hours? This will sulphate it up on you.

Have you used a cheap chain store (Super Cheap etc) charger on it? These can over charge the battery and boil the water out of it. If you use one of those chargers you should halt the charging before the battery becomes fully charged

To charge and maintain a deep cycle battery you really need a good three stage charger and/or a large solar panel with a good controller like MorningStar.

PeterD

It's a maintenance free battery you said, so apart from charging it after use there isn't much you can do. Agree with the slow charge comments above. How do you know it's stuffed? Get a second opinion - they may just be trying to sell you a new one unnecessarily.