hmm, true. I didn't even click. Ignore everything I said.
We have a few old telstra deep cycle and sealed batteries and charge them with both a ctek and cheap kmart charger and haven't had any issues. touch wood.
However, if its reading 10v which is pretty low, personally I'd just buy a new one. It's 4 years old now so it could be on its way out and may cause you less hassles in the future just replacing it now.