Main problem I had was getting it to start...mainly because the MC28 needs some power so it could read the card to actually turn the ignition on. The MC21 has a mechanical iginition so I presume this wouldnt be an issue.

On another note, I remember Tom not being able to get a certain race MC21 to start at all with a flat battery, as soon as fontyyy robbed a battery from his spare bike it started up.

Not sure where the conclusion is in that, but I really dont think it will cause any damage as its usually a too high current that breaks things, flat batteries would be too low and a quick run around the block usually gives enough power to get things running properly again.

Faulty recifiers have been known to destroy batteries though by over charging them, then they dont hold any power at all.