Battery dead after 6 months.

[Ihavenojob]

My daughter has an Aygo, the battery was replaced mid 1st lockdown as it wouldn't hold a charge. New battery fitted and it's been fine up until a week ago. Went down to hers and jumped it, let it run, then she took it for a 5 minute drive, and when back I checked the charge voltage, fluctuating from 13.4-13.8 on tickover, so turned it off. About an hour later, she went to use it, and totally dead again. Do you think the battery has had it, or the alternator is not charging enough or we didn't run it long enough ? I thought there may have been a draw on the battery or a short, but if that was the case I'm sure it would have died months ago.

 

[Burnerman]

5 mins isn't really enough to fully charge the battery, so give it a chance by charging it up and testing again.
Ideally you are looking for around 14.5v if the alternator is in good nick.
No lead acid battery should ever be left flat- if it has it will be low on performance.
John

 

[sxturbo]

How many miles does she travel on each journey

 

[Ihavenojob]

How many miles does she travel on each journey

It doesn't get used much, but most journeys are 20 miles plus.

 

[Harry Bloomfield]

It could be the battery is pulling the alternator voltage down, but as Burnerman said it should be upwards of 14v.

Can you put the battery on charge for 24 hours, then see what voltage you get.

Modern cars should never be left longer than a few weeks, without the car being given a decent run to bring the battery back up to full charge. The alternative is to put it regularly on a charger, to maintain the battery. It helps if the car cannot be used, to disconnect the battery from the car, because all modern cars draw some current when parked to power the electronics.

 

[sxturbo]

Be careful on the volts, I'm not 100% on this particular model, but most cars these days have variable voltage alternators, this is for emissions and reduced engine loading, so the volts on idle could well be different to what they would be when the engine is running under load.

Not sure if I've explained that clear enough..

 

[ericmark]

I hope by now all is fixed. The last two posts are correct. However I have found it can take a weeks to fully recharge a sulfated battery.

But also over charging can also kill a battery.

So it seems we are forced to buy stage chargers now renamed "smart" chargers, when I started they were only used on fork lifts and the like, but today we have a lot of chargers designed to charge at what seems a very low rate typical 3.8 amp dropping in stages to 0.1 amp and finally off.

I have an energy meter so can monitor the charge rate, wife's Jag took 10 days before charger auto switched off. I have two cheap Lidi units which move battery to battery.

The other option is content voltage, which takes longer. Around 13.4 volt will recharge a battery, but normally we use 13.8 volt, it is a compromise so the smart charger alternates between 12.8 and 14.4 volt, so at 14.4 charge rate drops and at 12.8 it raises, we are told this is better than constant voltage, but there seems to be some debate over this.

However in the past found old CB power supply works well.

 

[Peter.N.]

On some vehicles you cant get 14.5 v on tickover, although I'm not all that sure about this modern stuff, try revving it gently, if still low voltage the alternator could be faulty and leaking current thus running the battery down. Connect an ammeter in series with the alternator cable - disconnect it and connect to two ends across the meter.

Peter

 

[ericmark]

I stopped being an auto electrician in around 1995, and I was mainly commercial, straddle carriers and the like, designed to lift and carry 200 ton. But most alternators at that time were designed to be 13.8 volt on a 12 volt system, you can get special regulators which can stage charge, or even pulse charge, so some systems can go to 14.8 volt, but would only expect to find that on a narrow boat.

So over 13.2 volt and it's charging, in the old days when head lights took a lot of power, if the voltage stayed when the head lights were switched on we said good enough, but today when engine management controls charging not quite that easy.