Battery Stuffed?

Put it on the charger then take it to your Auto leccy and he should load test it for free - That will reveal all

You can never rely on a voltage reading to tell you if a battery is fully charged or not. It may read a full 12V static, but when you put a load on it, then the reading will change. Like the previous post said, load test it for a proper diagnosis.

Steve, this may not be quite technically correct, but here goes. With all the bouncing around that a battery does, somebleepty stuff falls off the plates and collects on the bottom which could sort of short out the bottom of the plates. I've often thought of turning over the battery and shaking out all that loose stuff and then re-fill and charge. Has any-one else ever tried this? or is it not worth #!@ing about with it?. Rus.

Steve,
I gather that the aux battery in the camper is the prob, do as the others say and if it is RS. then get a glass mat battery to replace it, a little more xy than the normal wet cell but they are the best IMHO for campers and caravans.
Mine has done three years continous work in the van and been very low on charge many times but still comes back.
Try this site.
www.solaronline.com.au

Yes , i can almost garauntee the battery is shot. Considering that 12.8 volts is fully charged and 11.8 volts in 20% remaining approx. the fact that you read 9 volts is testiment to the fact its finished. Has it ever been left sitting in a discharged state? Remembering that deep cycles actually self discharge over time. This is the most common cause of premature battery failure.

The other thing to consider is how far are you discharging that battery on a daily basis. If you are running a twelve volt fridge than i would suggest it is much too small. The reason is that the deeper you discharge a deep cycle the less number of cycles you will get in total.

Dodger is spot on in regards to AGM's. They can handle a larger percentage of there overall state of charge at one time. So, an hours driving will put alot more into an AGM than it would into a classic lead acid.

When a battery is heavily sulfated due to being left sit etc. There is one thing worth trying and thats an equalisation charge. Most 3 stage battery chargers are capable of this and basically its a controlled boil. This should only be done for a max of two hours but generally works well. I do this at work constantly and have bought many batteries battery to life. Give this a go Steve. Let me know