I am new to old bikes.
I have a c15 and it's won't start every time.
I am thinking its the battery is failing .
If I attach a charger to the battery it will sometimes start up.
Thoughts
generally, on older bikes the battery was there for storing power for the lights. we had to put up with dimming lights when coming up to junctions.
today the battery is used for everything.
there may be a emergency position on the switch which would allow starting without battery power, taking power form the generator.
what year ceefer?
has it had any modifications?
at that age, any of the connections could be failing or the generator rotor may be losing its magnetism. points? have they been gapped? coil subjected to damage?
With any bike, whether modern or classic, the battery needs to be kept in good condition. If you haven't used the bike regularly, or kept the battery fully charged using an intelligent charger when not being used, then the battery will almost certainly be duff and will need to be replaced.
The problem is that lead acid batteries ideally need to be kept fully charged at all times. If you allow them to remain partially discharged for any length of time, lead sulphate formed on the plates will start to crystallise and, once the crystals are formed, you can't reverse the process by charging the battery leading to a reduction in the battery capacity. This means that in this sulphated state, as soon as you try to draw current from the battery, the battery voltage will drop very quickly.
It is a big problem keeping classic bike batteries in good condition unless you have invested in an intelligent charger! A good test of the condition of the battery is to switch on the headlight with the engine off and see how long it takes to dim. In this case, it is likely to be a few seconds confirming it is duff!