I think it depends a lot on how good your charger is.
I've had to put up with a crappy halfords 5amp job.
The charge level drops to 0 after about 5 hours, but I can't see it's been charged fully by then.
Not sure if that means the batteries knackered, or the charger won't do the job.
I always leave it on for hours after, in case there's something trickling in.
I'm not going to bother getting a new battery until I can afford a good charger too.
Might as well get the best out of a new one.