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Battery voltage low, alternator voltage high

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Author Post
Mon Jun 04 2018, 03:30pm
Member No: #42824
Joined: Nov 29 2015
Location: Cardiff
The day after a 160 mile drive, the battery voltage reads 12.2 Volts.

With the engine running it's 15.6 Volts.

All is not well methinks! That could explain why the Eco only kicks in after a 100 mile drive.

Back to the dealer tomorrow
Tue Jun 05 2018, 10:09am
Member No: #42824
Joined: Nov 29 2015
Location: Cardiff
I decided to take it to Halfords for a free battery check. No surprise that they deemed the battery to be @ 53% and not in a serviceable condition and they would sell me a replacement for around £250. I declined their offer and proceeded to my dealer.

I had to wait for just over an hour, to be told that the battery was OK but only 70% charged. It had a 20 mile trip to get there, so with the voltage at 15.4 volts, I would expect it to have taken some charge.

I asked about the alternator output being @ 15.4 volts and was told that it is probably working overtime to charge the discharged battery, but had not checked it. They seemed not to grasp that the battery had not held its charge after its long journey.

They are going to have it in and charge the battery overnight and then check it the next morning, but that is not going to happen for 3 weeks.

I would think that it will show that it is fully charged in the morning. Hopefully they will then wait to see if it loses its charge over the rest of the day.

They need to put the battery trough all the tests to cover themselves against wrongly changing a battery under warranty and then not getting the money for it.

In the mean time, I'll be carrying out the same battery checks at home, to see what's occurring.
Sat Jun 09 2018, 05:29am
Member No: #42824
Joined: Nov 29 2015
Location: Cardiff
I've installed a voltmeter, which cost just £0.98 - Click Here -
wired to a car 12 volt plug and plugged into the socket in the accessories compartment.

This displays what the 12 volts is doing while I drive, with interesting results.

It showed that with the engine off, the battery was at 12.2 volts, same as on my multimeter and with the engine running 15.3 volts.

These voltages stayed constant.

I decided to put the battery on charge with a smart charger, which showed that it was 25% charged. It gradually increased the state of charge, and after 48 hours - that's 2 days it was only showing 75% charged but had got to 14 volts on the charger display.

I disconnected the charger and the battery voltage was at 12.6 volts, but was not constant, but falling. I started the car and the volts showed 12.3 volts. I took it for a drive and the volts went up to 12. 6 volts when under power, but the strange thing was that when I took the power off (over run) the volts went up to 15.3 again. Power back on and the volts drop to 12.3 again.

I think the regulator is defective, which has in turn killed the battery. Happy days!
Sun Jul 08 2018, 04:06pm
Member No: #42824
Joined: Nov 29 2015
Location: Cardiff
Well, it's been in and after 2 days - No fault found.

It still charges at 15.3 volts but not for as long. The up and down voltage now stays constant, regardless of power on or off.

The Eco has worked every day on every trip. They must have done something, even if they didn't knowingly do it.

So, all good so far.
Thu Jan 09 2020, 04:55am
Member No: #54589
Joined: Sep 10 2019
Location: London
Hi, sorry, I know a bit of an old thread but I assume that the car was then fine? Mine also runs at about 15.3V with the engine running (about 12.5V without engineer running) and not sure whether an issue with alternator or a short circuit somewhere. It intermittently gives me random faults too.
Thu Jan 09 2020, 09:06am
Member No: #42824
Joined: Nov 29 2015
Location: Cardiff
The only change is the Eco is back to only working after a 150 mile drive.

Everything else is working OK, apart from intermittent mirror adjustment. The battery still loses its charge too quick for my liking, just as it has always done, but it always starts.

I'll only really be sure that it is a battery fault when & if I have to buy a new battery.

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