I think you're in the wrong section I think you're talking of a Single cylinder one?
Number one check the battery for electolyte if the levels are low it won;t store charge
IF you jump it to get it running get a Decent multimeter on the terminals A battery should be around 12 to 12.5 volts if it's okay (General figures folks you meter may read higher / lower etc etc If you're in any doubt take it to a garage)
When the bike is running and charging it should jump up to 14 ish volts and as the charge tops up it should fall back down to 13 13.5 ish If when your mates is running you may find 15 or higher volts
This will "Usually" mean that the regulator rectifier will be stuffed (and probably the battery too!)
