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Is my battery getting over charged?

Started by Nifty150, May 02, 2022, 06:45:08 PM

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I recently purchased an lead/acid battery and it went bad after running the bike just a few times.  I have now purchased a new Agm battery.  When the bike is not running the battery reads 12.9v, when the bike is at idle (1,100 rpms) it reads 13.5, when rpms increased it will peak at about 15.2 volts.  I'm thinking 15.2 is too high.  Looking for suggestions.  I do not want to ruin another battery.  Is my voltage regulator bad?, if so what are my options.  Any help would be appreciated.



I am happy with this:

Other people prefer an external voltage regulator to get it away from the heat.   These bikes are 29 - 38 years old at this point.   Even if the heat kills the new voltage regulator in "just" 10 or 20 years, I'm okay with that and will simply replace it again!


I recently had my carbs rebuilt by Randy and sent him the same inquiry.  I imagine he will get back with my tomorrow.  Thank you!  I'm pretty sure this is what I need to do.  It helps bouncing problem off of a few people.  I have viewed the how to video and it looks pretty simple.  Error 404 (Not Found)!!1

Pat Conlon

If you read the Li or AGM battery specs, you will see that they specify a max charging voltage of 14.4 volts.

So yes, 15+ volts is too high for the new generation sealed batteries.

On the stock old school lead acid batteries you would just boil off the problem, just add more distilled water and you're good to go...No so with the sealed batteries

I can't imagine a worse environment for the VR than where they are located. No wonder they go cuckoo.
1) Free Owners Manual download:
2) Don't store your FJ with E10 fuel
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire:
Fuel line:


RPM saying they are out of stock.  Anyone have links to external Voltage Regulators and instructions for install on 1990 FJ1200?  I will keep searching for related discussions.

Pat Conlon

1) Free Owners Manual download:
2) Don't store your FJ with E10 fuel
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire:
Fuel line:


   Brad, I had a similar problem a few years ago. I replaced the voltage regulator, made no difference.
I found the problem and I am pretty sure that most FJ's that charge around 15-15.5 volts have the same problem.
The regulator gets it's signal voltage from the power wire that powers the instrument panel plus other items, it's reading  lower than
actual battery voltage, therefore over-charging to compensate.
The fix is relatively simple. You need to cut the brown wire going to the regulator and connect it to a switched relay. The relay must receive
the switching power from the ignition switch (you can use the other end of the brown wire as the switching power), which in turn connects the brown regulator wire directly to the positive battery terminal via the relay.
This means the regulator will only read the actual voltage at the battery. Since doing this mod, my charging voltage is at a very constant 14.1-14.2 volts.
I have a permanent voltage meter in place so I know it's working well.
  Regards, Pete.
1985 FJ1100 x2 (1 sold)
2009 TDM 900
1980 Kawasaki Z1R Mk11 (sold and still regretting it)
1979 Kawasaki Z650 (sold)
1985 Suzuki GSXR 400 x2 (next project)
2001 KTM 520 exc (sold)
2004 GasGas Ec300
1981 Honda CB 900 F (sold)
1989 Kawasaki GPX 600 Adventure


Quote from: oldktmdude on May 04, 2022, 06:05:48 AM
  Brad, I had a similar problem a few years ago......
  Regards, Pete.

Good call Pete.
"Tell a wise man something he doesn't know and he'll thank you, tell a fool something he doesn't know and he'll abuse you"

mike g

Just checked mine and it seems to be over 15v
checked the voltage at the red and brown wire, they were close, but the brown was lower by about 0.2v,
so tried jumping a wire from the battery down to the brown connector,  voila 14.8v max (as per the manual).
I've ordered a relay, just hope the voltage drop isn't too great.
wondered why the batteries didn't last more than a few years!

had a problem with my DT charging at 8+ volts and gone back to lead acid for that after the last 2 motobats died, the last one was still under waranty, so will see if it's refunded

mike g

fitted the relay now charges at 14.5v - happy days