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[Brush]

My 56 Bullet has been converted to 12 volt really for safety. It has not been used for a while and I recharged the battery about a month ago. My reading now shows 12.5 volts across the terminals with my voltage tester. The bike is magnito driven and starts very easily and runs excellently. My question relates to also having a 1973 BSA 650 A65 OIF (again 12 volt battery)which I took out for a run yesterday for about an hour. My reading for its battery is now 13.5 volts (prior to taking it out it was down at 12.45 and not easy to start). This low reading was the reason for taking it out. Now its fine starting wise. I wonder if there is however a problem in that the bike may be overcharging or whatever. There are no obvious electrical problems as everything works fine - lights, indicators, horn and electronic ignition. I am sure I read somewhere with electronic ignition the battery has to be in good condition and hence the starting problem.

I am wondering if there is an issue which could cause battery problems even a severe failure (e.g. being really hyper cautious split case or whatever and acid everywhere). I wonder if anyone on the forum can advise maximum capacity of a 12 volt battery (6 cells) to put my mind at rest although there may of course be nothing wrong but obviously as with us all I want to minimise any issues in my custodianship of both bikes.

Regards to all and thanks in advance for any advice offered and looking forward to some warmer weather as yesterday's ride was freezing!

[Frank]

A battery in tip top condition will give a voltage of 12.6v, 1.2v per cell. If you were getting 12.5v after a period of rest I would say that was Ok. The charging system will charge the battery at about 14v and if you measured the voltage soon after a run the battery voltage would be around 13v but would settle down to it's nominal value of around 12.6v with time.It doesn't sound as if you have a problem . Electronic ignitions do need a minimum voltage to work and if the battery is subjected to a heavy load when starting, e.g with an electric start, there may be some difficulty if the battery has not the capacity to to maintain the voltage. That capacity is the crucial thing but as a rough guide I would say that 12.5v after a period of rest indicates the battery is not too bad.

[PeteF]

The capacity of the battery (amp hours) will depend on it's size.
To check if it's overcharging, take the voltage at the battery with the engine running. When revved it shouldn't go above 14.5v. If it does go over that you may well have a fault with the voltage regulator. 12.45 seems to me to be fine for a battery at rest but the real test is if it holds that voltage when you put a load on it (lights for instance) without the engine running.

[Frank]

Sorry I got the maths wrong. each cell gives 2.1v, 2.1v x 6 = 12.6v

[Brush]

Thank you all - very grateful for the advice and your time in giving it as it is gratefully appreciated. The voltage on the battery has now dropped back to 12.6 having rested over night. I did check it yesterday just after I got back to register the 13.5 as suggested in the replies. As said I am very grateful for the comments received as extremely helpful and they will also help me monitor/controlling things going forward. As you can all probably tell I am in learning mode with these bikes. Take care all.