Motorbike electrical issue

raymond00001, Sep 30, 12:25am
Probably needs new battery but wondering if rectifier is a bit buggered too. GSXR750 done 96000km. Doesn't get used much and sometimes needs a charge between rides, battery about 7 years old. Runs fine then sometimes won't have enough grunt to start while out on a ride, bump starts ok. Have checked the alternator output, ok as per specs. Done the resistance tests etc and seem close enough to values.
At rest/off battery shows 12.6V, when running at idle showing 13-13.2 like its getting a charge ok, but rev and voltage drops to about 8! but runs ok still. Alternator showed 40 AC at idle and then 74V when revved as per manual.

taipan4, Sep 30, 12:40am
give it a good run so battery is fully charged & leave over night with battery connected & check voltage before you start it the next day and then do the same the next day but disconnect battery at night & check voltage the next day this should eliminate faults other than battery (like something draining the battery)

msigg, Sep 30, 2:36am
yea sounds like battery is too old.Just buy a new one and get another 5 years out of it. If you keep stuffing around with the old one you will do more damage to the wiring system, waste of time. $200 get new.

skin1235, Sep 30, 3:05am
but rev and voltage drops to about 8!
recheck all the connections
thats typical of a loose spade or loose earth bolt on the regulator

raymond00001, Sep 30, 3:39am
Thats a good idea as I often take the battery out to charge it, maybe a cracked post or dirty connectors, sometimes its the obvious.

kaymay88, Sep 30, 5:46am
Your stator is poked IMO.

ceebee2, Sep 30, 7:29am
What was the DC reading by comparison!

raymond00001, Oct 10, 3:49am
Borrowed another battery and issue resolved. Seems the old battery (7 years) was so knackered it was acting like an electrical black hole and just sucking voltage. Weird as it would have enough grunt for one start after a charge and read 12.6V at rest.

peril787b1, Oct 10, 9:43am
Very odd that your battery was stuffed after 7 years (note sarcasm).
That would have been my first target of investigation. A battery is a cheap option compared to a new rectifier/stator

raymond00001, Oct 10, 5:23pm
LOL yes, but it would crank over fine after a charge and randomly not want to restart after various trip distances.

berg, Oct 10, 6:47pm
Get yourself a c-tek battery maintainer for your bike. Have one on my ute and one on my bike and they keep the battery's fully charged and less suseptable to failure. Have had similar battery failures as yours in the past and they can be a bugger to find