The battery simply won't hold a charge of 14 volts, around 13 - 13.5 would indicate a fully charged battery. If it drops much bellow that then maybe indicative that it is failing. I usually buy my batteries on line via ebay, I think I paid about £10 for the last (Yassa) one.
I am wondering though if you have a disconnection in your loom now though as with even a reduced charge, the lights should come on.
