'Lecky 12V gauge

[oldbilbo]

With two batteries fitted, controlled by removable keys.... while engine-charging....

With 'One' selected, the indicated V is 14.... rock steady.

With 'Two' selected, the indicator flickers swiftly around 14V.

With both selected, the indicated V is 14.... rock steady.


What's going on and how do I fix it?

 

[LadyInBed]

Maybe bad connection on 2
Swap 1 and 2 round and see if fault stays with 2, moves or goes away.

 

[NickRobinson]

Do you have a VSR? It could be cycling/hunting.
My camper interior does 'disco' for an hour or so after arriving and stopping the engine.

 

[annageek]

Are both batteries engine start capable?

If so, does battery 2 still start it up without a struggle? It sounds a bit like a high impedance battery to me. Batteries are usually a nice, low impedance current sink that smooths any ripple out completely... until they become knackered and go high impedance.