Battery issues Citroen C3 Picasso

[Sarah1973]

Bit of a long one but I’m trying not to drip feed! I have a Citroen C3 Picasso 2016 Diesel which has only done 39,000 miles. I normally only do short distances to work and back etc. I drove it up to the Lake District in September and did a lot of travelling and it was running brilliantly. About 3 weeks later it wouldn’t start. I replaced the battery but still kept having issues so had a new alternator fitted. The battery is only charging to 12.4 volts when the engine is running. I have had both the battery and the new alternator checked and both are fine. I have had diagnostic tests done and nothing flagged up. I can drive the car normally for around 3 weeks then it won’t start. I charge the battery up and I’m good to go again for another 3 weeks. I’ve noticed a couple of times that my stereo will come on but no volume and at the same time the reverse beep doesn’t make a sound either. This has only happened twice in the last month and usually rectifies itself when I next use the car. I’m thinking it’s something electrical or a parasitic drain but would that cause the battery not to charge properly when running?
Any advice greatly appreciated thank you

[mickthemaverick]

Hi Sarah and welcome,
That sounds like a rather sad tale. It would suggest to me that you may have a faulty Battery Management System (BMS) which is in the engine compartment under the fusebox. As a first check I'd suggest you look over all the wiring and plugs in that area searching for dampness and/or corrosion. If you find any dry and clean them and then see how it goes. If not come back here and we'll look at the next stage.

[Sarah1973]

Thanks Mick I will have a look tomorrow when it’s daylight again! I appreciate your help

[Mihael_M]

Hello Sarah, if I may join the discussion. You should definitely check the BMS. This voltage of 12.4 V (if you measured it on the battery itself while the engine was running) is the voltage of the battery and does not receive charging from the alternator. The battery does not charge, so you can drive for a while until it is empty. Although it is strange that there is no light for bad charging on the instrument panel.

[mickthemaverick]

I did think about the ignition light too Michael, but I have a feeling that its feed is direct from the alternator output, so it will go out if the alternator is charging but the BMS is not connecting the charge through to the battery. I suspect there will be an issue in the BMS area so time will tell!

[PaulC5]

Check the voltage with the engine running and the lights and rear window heater on. If a smart alternator the voltage should increase above the 12.4 volts being seen without these switched on.