Hi Peter,
I’m not sure why changing the batteries would start this happening if it wasn’t before unless it’s down to volt drop across one of your remade connections after changing the batteries. You don’t say where (or how) you’re measuring it.
I found that the alarm on our 405 was going off at too high a value too and could not get any info out of VDO who make the panel. I and ended up removing the buzzer as I have a Victron smart shunt to monitor things and believe it to be more accurate anyway.
Dave
The membership association for owners of Dufour Yachts