JoeA
I have a 55020 10 kw that has been working fine.  Today I was going to change the oil and filter, planning to run it to warm up, when, the power failed.

But, no start.  Went out to look and the message was RPM loss, or like that.  Would not start manually, no nothing.  Then display went blank. 

Got out multi meter and battery was 10.4 volts.   Did a jump start and it started and transferred fine when I set it to "auto".

I measured the volts while running, never went over 12.4 while I watched for a few minutes.   The battery is several years old, maybe the original.  Went to research batterys and charging.   Then power came back on, so I went to measure the battery and it read 13.something.  OK.  I guess the charging works then, but I am confused as I though it trickle charged from the AC circuit, even when not running.  Guess not?

Then after changing oil and filter, it would not start, just clicking a bit.  So, the battery did not hold charge, I guess. 

Time for a new one?  Votes?  I'll bet the Aye's take it.
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Geoff Z
Put your meter on it and attempt a crank. Your voltage may dump. If so you have your answer. 13v sounds like the charger is working. If you don't know the age of the battery and it could be original, probably time to change anyway. Not the best idea to jump the generator. You are introducing a stray voltage into the system. We have seen controllers damaged.
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murphy
Treat the generator to a new battery.  If you want reliable emergency backup then change the battery every three years.  Don't wait for it to die.

Your 10.4 volt reading right after the power failed screams dead battery to me. 

I've replaced lots of UPS batteries that read good voltage with no load but put a 100 amp load on them and the voltage drops to zero.
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Geoff Z
+1 with murphy: voltage drops = amps rise = starter heat and strain = shortened life span

So many people take their battery to the edge before replacing. Lucky that these generator
starters are not required to perform more often or we would be experiencing a much larger
replacement volume.
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JoeA
Apparently my default setting is to not get notifications, so, after a bit, I just lugged the battery to a parts store for a test, just to be sure.  Definitely bad.  Amazing it decided to just "drop dead" like that. 

New battery did the trick.

Thanks for the replies.
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