Intermittent Battery Charging Issue

[SamLJ]

2011 Peugeot 308 1.6ehdi with stop/start

Hi all have a strange intermittent charging issue.

Car normally charges at 14.7volts. However occasionally the voltage will drop to 12.6 roughly. However when on overrun or strangely activate wipers, the voltage goes back to normal, then drops down when driving or at idle. No fault codes present in bsi, ecu, or bcsu.

Looking at live data in ecu there’s two readings;
Controlled alternator regulation voltage
Battery charge voltage setting

It seems like whatever the ‘battery charge voltage setting’ is showing, the ‘controlled alternator regulation voltage’ follows it, so thinking whatever controls the battery charge voltage setting could be at fault, but I’m unsure what controls it.

I have noticed that when I pull F3 fuse for the battery charge status unit, the charging voltage goes up to 14.3, so does that point to a fault with the battery charge unit on the negative terminal? Even though there are no fault codes. Also noticed if I tell the car that the battery has been replaced the voltage goes back to normal even after letting the bcsu recognise the battery overnight, and sometimes presents a U1218 Intersystems CAN fault straight after battery reset, which once cleared doesn’t come back.

Battery is a 096 AGM 760CCA which is only a year old and seems to be in good health and have performed BSI resets which don’t seem to have any effect.

Many thanks

[Huskyxantia]

There was something similar on here a while back I think it was the regulator on the alternator that was packing up.

[SamLJ]

I really hope not not at £1000 to replace

[PaulC5]

If it is a smart alternator these can vary the voltage depending on the load. When at the lower voltage switch on the headlights and window heater and see if the voltage goes up - if so this could well be normal and nothing to worry about.

[SamLJ]

Not sure if it's a smart alternator but in the 7 years I've owned the car it has never done this, I've tried putting on heavy load but didn't make any difference, just frustrating that there is no fault codes. It has a reversible alternator so not sure if that makes it smart