Hmmm
'smart' changers ... I'm getting fed up with mine ... I'm an electronics engineer by training, and the 3 different ones I have all get it wrong for pretty simple things.
Personally, I hate the optimate, cos it promises the most and delivers ... quite a bit less than that ( I have had several batteries that it has said were crap which have charged perfectly with its cousin the simpler 'ultimate')
Because the chargers monitor the battery terminal voltage differently according to what amount of current they are putting in, different things can confuse them.
My latest problem has been that those stupid right-angled bits on my 748 have had the horizontal-bolt-bit start to come out (couldnt feel them tightening properly), which caused just a bit of a bad connection, and hence about 0.2V extra drop on charge which caused the charger to short-cycle in and out of boost and maintenance mode. (Sorry to go on, but that means its not good !)
If you have this kind of problem it will prob mean that the bikes reg wont charge the batt properly either !
ALWAYS CHECK ALL THE BOLTS FOR TIGHTNESS FIRST !!!
If you read the leaflet it'll tell you the voltages it is working on, and they are the numbers you need to look at with a voltmeter to tell if the battery is still ok really, just 'past its best'.
You have already worked out the 'acid' test (sorry) which is whether it turns the engine over !
The time to really really change the battery is when it makes the sprag-starter chatter - that means some horrible wear is happening inside the left hand case which is to be avoided !
(Rant over)