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Hello there, I bought a YZF R-125 3 weeks ago and battery died one week after I bought it and it needed to be recharged.

I recharged it about 2 weeks ago (left it overnight) and today while I was riding the check engine light turned on. The motorcycle was working normally. When I got home, I checked the check engine light flashes and it was error 46 again (just as it was before battery died).

The motorcycle has a Yuasa 12v 9Ah battery, is this not a good one? I heard 5.5Ah should be normal for a Yamaha YZF R-125. I don't know if it's the regulator because the check engine light went away after I recharged the battery.

Do I need to replace the battery or is it something else?
I don't know how old the battery is, I know that it has been changed after winter has passed

Any help would be appreciated. Stay safe y'all
 

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2008 YZF-R125 (180cc)
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Have you got a multimeter? if not, get one, and check the voltage on the battery when the bike is off.. should be around 11.8 v or so, and when the bike is running it should be charging and you should see a value of around 13.8v or so.

If you're not getting the higher value when the bike is running then that would suggest a problem with the charging system - could be as simple as the rectifier isn't plugged in properly (e.g. corroded contacts, just forgot to plug it in after tinkering in that area.. it happens).

I got one of these (link below) and have it permanently installed on my bike - you'll see it in my videos where it's mounted on the front fairing stay (just in front of the ignition).. so I see the voltage when I switch the ignition on and start the bike, but it's not staring me in the face the whole time when riding... but it means as soon as I switch the bike on I have an idea of the state of the electrical system, whcih gives me an early clue if i've forgotten to plug the rectifier back in or if there's a problem.


There could be other problems wih the charging system - but they're all a bit more complicated so i'd start with the basics like corroded contacts and "is it actually plugged in (properly)", since most fo the time it's somethgin like that than [insert something more obscure/worse].

Hope that helps :)
 

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the battery should be 5.5 Ah. When the battery is bigger (Ah), the alternator cannot charge it.
Check the battery charging as advised by a colleague above.
 
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