Hi Rob. You will find a wealth of information on this board (maybe you already have ...) that you rarely get from wheelchair suppliers. The pinned thread on lead batteries is useful.
viewtopic.php?f=2&t=3609Such as what voltages your charger should be doing, but probably isn't. Remember for a 24V battery like most wheelchairs have, there are 2 X 12V batteries wired in series. Which nobody had ever told me before I got here, so all the info was very confusing.