Strange battery charge problems
 

I know the Volvo charge regime causes odd battery charge issues.

I keep my infrequently used V60 Polestar on a charger ( CTEK 7.0), which keeps the battery on full charge.

Before I started it today, the charger was indicating it was fully charged. 12.95V on the plug in voltmeter in the centre console

I started it with the charger still connected, the indication changed to partially charged.

The plug in voltmeter in the centre console indicated 12.1V, no change when I revved the engine.

What on earth is going on ? Another dead battery ?

If you're testing a battery, test the battery terminals.
If you're testing alternator output, test at the alternator b+ post.

Testing anywhere else further down the system like fuses and power sockets just adds an extra level of uncertainty which would then need verifying at the battery or alternator anyway so cut out the middle man.

[QUOTE=cheshired5;2745344]If you're testing a battery, test the battery terminals.
If you're testing alternator output, test at the alternator b+ post.

Testing anywhere else further down the system like fuses and power sockets just adds an extra level of uncertainty which would then need verifying at the battery or alternator anyway so cut out the middle man.[/Q

I just have to accept this car ( maybe all Volvos) of this age are strange.

The voltage using a multimeter directly on the battery, is near as dammit that shown on the plug in voltmeter ( 0.01V different).

Sometimes 14V+, sometimes 12.1V

I keep it permanently on charge; 2 days off charge and reconnecting the charger, it indicates the battery is seriously discharged,

I believe that for the purpose of fuel efficiency the alternator only produces charge output whilst the engine is on the overrun.

My next step would be to test the alternator output directly as previously described to see if the output voltage has similar behaviour.

If alternator output is consistently above 13v, something odd is happening between the alternator and the battery or with the battery itself.

The electrical system Design and Function section of Vida might shed light on exactly what normal behaviour is.

^^^^^ That (or something of that ilk)

With the battery at 100% charge, the system will likely not apply a normal charging output until the SOC drops to say 80% or something.

Good point, the alternator will not provide charge if the battery is already over 80/85% charged. VIDA or even cheap diagnostics (ELM327 with Car Scanner app) will show this percentage.

Got round to checking Vida and there is nothing relating to a high battery state of charge stopping alternator output so where exactly is this information coming from?

A depleted battery or cold conditions would result in a higher alternator output voltage once out and about but that's standard on pretty much every car charging system.

From the Design and Function section which I recommended should be checked, there can be little to no alternator output following starting of the engine and on occasions where the engine is idling but at higher RPM, there's nothing to suggest that alternator output will be anything other than what you'd expect to see on any charging system i.e. above 13.5v
Nothing about no alternator output if the battery is charged above any percentage let alone the very specific percentages you've mentioned.
Nothing about only charging on the overrun.

Maybe on the occasions where OP was receiving battery voltage only, it was because the engine was idling in which case this is in line with how the system is designed to work.

The battery's condition is irrelevant as far as I can see but I'm always happy to be corrected and learn more.

Perhaps the OP could observe voltages at various engine speeds and electrical loads and on a drive to fully describe the system voltage behaviour.

If it was easy to do so I'd find the relevant forum thread and post a link to the specific post where a former Volvo technician gave this information. So for now it's from my memory.

Regardless of source, I have to say that it made no sense hence why I looked a little deeper into the system design.
Fortunately OP has a good battery at effectively full SOC so hopefully he can report back live voltage data particularly out on the road.

If system voltage is regularly >13.5 whilst driving (as Vida suggests it should), the no alternator output theory would only appear to exist in the ether.