Maybe the rectifier (which charges it) is ****** and you have just used all the power out of it. It would last a fair while on just starting it once a day.
Charge it back up and get a spark to put his testers on it. it should say 12v then when you start the genny check it again and if its higher than 12 volts then its charging.
Haven't tried charging it jenks we're jump starting it off the van and when we turn it off and try it again we get zilcho, if we get it running and get a sparky to test it and then it says more than 12v does it still mean it's charging?