Volvo D4 apparent overcharging battery

[Nigbb]

Has anyone experienced this or have any ideas?
I have twin D4.260's that after about 45 mins run out both suddenly showing an overcharge on the battery volt gauge, about 15.5v (in the red section) . The reading was a bit erratic dropping back and then rising again, I did stop and re start each engine in turn but still showing in the red.
However in the digital display which shows the engine systems which can be scrolled through via the EVC the volts was always the normal 14.2v, I headed back in and by the time I was tied up all had settled down again and the gauges corresponded with the EVC digital readout in the tacho's .Can anyone explain this? Should I be worried? Any ideas?
Cheers Nigel

 

[vas]

had that with old VDO analogue voltometers - a trim resistor in them had gone and the needle was just wrong (showing 29-30V when it should have been 25V).
If yours are indeed analogue, you could pull one of them and measure with a multimetre what it's measuring when it's showing 15.5V. And anyway, I'd go with what the electronic display shows and not the needle...

 

[Nigbb]

had that with old VDO analogue voltometers - a trim resistor in them had gone and the needle was just wrong (showing 29-30V when it should have been 25V).
If yours are indeed analogue, you could pull one of them and measure with a multimetre what it's measuring when it's showing 15.5V. And anyway, I'd go with what the electronic display shows and not the needle...

Thanks for that, yes I was tempted to just pay attention to what the digital display is saying but wanted to make sure I was not missing something.
Cheers Nigel