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2004 BMW R1150R, 2017 BMW R1200GS, 2020 BMW S1000RR
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I was resetting the service interval on a 2017 GS using the GS-911 tool. When everything was connected, the diagnostic tool flagged the battery as having 12.1v available (motorcycle engine was off). Battery/motorcycle had just been disconnected from a battery maintenance device. So I figure, better safe than sorry, might as well get a new battery. The battery is taken out and just for grins, I use a volt meter to re-measure the voltage. With the voltmeter, it reads 12.7v. So which value do I trust (battery is 5 years old)?

Thanks in advance.
 

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You can not get a good reading on a battery without a load on it. That is why there are special battery testers called load meter test.

5 years is a very good time of a battery on a motorcycle. Hope you can get 5 out of a todays batteries.
 

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BMW_388 is right, but more to the point for you is this basic electrical fact. When you are using your GS-911 you have to have your ignition on, that turns the bike's electronics on, the fuel pump on, the headlight, etc. Your battery is then on some load with no regeneration happening unless you start the engine. Had you turned on the engine on it may have read 14.1v or so, even with a dying battery. I'd say 12.1v on a battery with no charging taken place and a load on it is one thing, and the same battery with nothing connected at 12.7v is absolutely normal. Maybe low, and not good, but a normal reaction. That make sense? I have a hard wired USB/charging cord in my RT's tank bag that has a built in volt meter and these type of readings are exactly what I see. Unfortunately with your RR and GS, you can't see the unloaded voltage with a GS-911 because it needs power to work.
 
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