Battery on 690 randomly draining while riding - Who has a good suggestion?

[Amsterdam]

Every once run a while I get a call from my son - "Dad, my 690 is dead again".  This call can come from his house or when he is riding somewhere.  When you turn on the ignition not even the dashboard lights come on or they come on and go through that low voltage routine.  Just a few weeks ago this happened again and I put the working battery from my 701 in his bike.  After that all was fine again for a while.

Yesterday I picked him up in Newlands, same issue.  He was riding along, slowing down for a traffic light and the bike cut out.  It was too dead to even swing the motor over once.  The battery voltage was at about 11V.  After pushing the starter button you could hear the relay click and the voltage dropped to about 2V.  It then came back again to about 10V after a little while.  I took the bike home and put it on charge, and after a while it starts again as normal.

The voltage while the engine is running, measured on the battery terminals, is 14.5V.  I have had the bike here before and it has stood for a month or more, it starts just fine on the first push of the button.

So, what can it be that that causes this?  What should I be looking at, measuring, replacing?  As with many 690s, the seat pan is broken.  Can this cause the problem by possibly pushing down on some of those relays just behind the battery?

 

[Mpandla]

 

[onderbroek]

 

[Colin Kaapschehoop]

 

[Operator]

 

[Colin Kaapschehoop]

 

[Amsterdam]

 

[Black_Hawk]

 

[Operator]

 

[Amsterdam]

 

[Black_Hawk]

 

[geopat]

 

[Amsterdam]

 

[Black_Hawk]