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Discussion Starter #1
About once a week I have to jump start my 2017 Prime. At first I thought it was a bad battery but after doing voltage checks I'm not so sure.
The battery when charged is at 12.6 which is good. When starting the engine it drops to 11 volts, from the research I've done also good.
When checking the voltage with engine running the voltage varies all over the place from as low as 11.3 up to 15 volts especially when revving the engine.
Most of the time the voltage does not go higher than 13.3 V
Is there a way of telling if this is the regulator or alternator. If the regulator is located inside the alternator then it does not matter, I'll have to
replace both.
Could a belt cause these symptoms?
I checked the engine running charging voltage on my Hyundai and a Fiat and both stayed locked at 14.4 V
 

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I would also do a load test on your battery. If you don’t have access to a load tester, any auto shop can do it for you for free.
 

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It sounds to me like your alternator is OK as the voltage seems to go above 13v and stays there when rpms are sustained. I would agree in load testing the battery, a good early test that is usually free from most auto parts stores.
 

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I would first test the battery. If it checks out okay I would then check the alternator. In most cars you can connect a multimeter to the battery cables. If you're under 13 volts at idle with no accessories on then your alternator may be on its way out.
 

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Discussion Starter #5
It sounds to me like your alternator is OK as the voltage seems to go above 13v and stays there when rpms are sustained. I would agree in load testing the battery, a good early test that is usually free from most auto parts stores.
Today I thought I would go for a drive with the meter attached and monitor the voltage. To my surprise it locked in steady at 14.6 V Only when Idling was it all
over the place. I will have a load test done on the battery tomorrow.
 

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Today I thought I would go for a drive with the meter attached and monitor the voltage. To my surprise it locked in steady at 14.6 V Only when Idling was it all
over the place. I will have a load test done on the battery tomorrow.
Please like me know what you find out. I have that happening also with a brand new battery in it. My battery light goes on sometimes 11.9 12.1 12.9 13.6 14.3 Sometimes It will start up with 13.6 or 14.3.
Or 12.6 than after sometime it stays at 14.3
[email protected] Thank you.
2009 Convertible
 

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Do a load test. Any auto supply store will do one for you. Your cars alternator from the alternator. should at least outputting 14.2 volts, with the engine running.

While the cars not running. A good battery should test out around 12.4 volts. Make sure you The Accessory alternator is tight, and in good shape. There’s no unusual sounds coming from the alternator
 

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Discussion Starter #8
I had a load test done on the battery and was told it was not the best but had seen worse. He also could not find specs for the original battery so set his load tester accurately.
I replaced with a new battery. I have not had any problems since, however I have been on a vacation and have not driven the smart car much since.
I'm still concerned about the varying voltages measured at the battery. It still varies from 11.3 to 15 volts. The service manager at a Mercedes Benz dealer dealership
does not feel the voltage varying an issue. Seems odd to me when both my Hyundai and Fiat lock in at 14.4 V all the time, driving or idling
As reported above, the Smart locked in at 14.6 V once when idling but that only happened once. It has since been all over the map with the old and new battery.
If the new battery charges OK with the varying voltages then I guess all is good. Time will tell.
Hats off to the Mercedes service manager. He went back and forth with me a few times by email answering my questions trying to help. Most dealerships would want you
to bring it in so they can charge big bucks and sometimes tell you you also need this and that done as well. When I do need service I will defiantly take it to him.
 

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... if all wiring grounds and alt connections are solid and clean start the car and monitor voltage at idle...then load the system while stilll at idle ...radio...lights...heated seats...it should not go below rated output fo charging

Jetfuel....like people all cars are different
 
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