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Well I seem to have an issue with my ’06 Street Bob. One of the cells in the relatively new battery went bad leaving the voltage bellow 12V. The question is how; was it a bad battery, or a voltage surge. Can’t test the voltage regulator without starting the bike and can’t start the bike without a battery. Any ideas where to proceed?
 

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Take the battery OUT of the bike......just for safety sake since you think it is bad.......and charge it up with a low capacity charger overnight.
If it is a wet-cell type, check it every couple of hours to be sure it isn't boiling over.
[edit] If the caps come off, check the water level before charging.

Next morning, disconnect charger then let it sit undisturbed for a couple of hours. Measure the voltage.

If it really has "a bad cell", it should read .....let's see.....12.6 minus 2.1 is 10.5.
If it simply wasn't charged up, it will be something between 10.5 and 12 now and 12.6 or a tad more when charged.

If it does come up above 12 when charged, the apply the "starter test".
If it turns over and runs, check the running voltage; should be 13.2 at recommended idle (put-put loping idle doesn't count) and a bit above that when rev'ed.
 

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I know you have some miles on that nearly 10 year old bike,have the stator and reg. been swapped out together as a unit yet?
Many times I've seen guys just do the reg and soon after have problems again, problems that can kill a relatively new battery.
H-D OEM stators from that period are usually good for about 60K miles and may pass an output test when cold but still be weak and failing while riding eventually leading to a reg and or batt failure.
If the bike has over 100K miles it's a good idea to do the rotor as well, one weak link in the charging system can get you back in the trouble zone again.
All done together with quality replacement parts you can expect about 100K miles trouble free.
 

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Oh it's bad. I can charge it, disconnect and watch it bleed off.
Maybe. Probably.
But that happens to some degree even with a perfectly healthy battery.
It depends on how FAR it bleeds down.
If it levels off at 12.6 or more, chances are that it is OK.
Even 12.4 might work for a while but is suspect.
 

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No they haven't been replaced, I'll look into that. The bike has 112k on it right now.
If that's the original stator at that mileage you did real good but even if it was replaced at some point (as said usually about 60K) it's likely due for one.
Again doing a stator & regulator together is the best bet, you won't save a dime if you replace one and the other causes both to fail.
 
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