The Datasheet from the Batteries to caompare with the Multisettings …
At room temperature, the end-of-charge voltage for a 12 volt lead-fleece or lead-acid battery with gel is 14.5 volts. The trickle charge of a lead-acid battery should not be higher than 13.3 volts
But still the question why the battery voltage suddenly drops to 52V …
It would be really important to check the voltages of the individual batteries.
Some winter sun now and batteries charging from solar, now climbing past 55V, no problem. That sudden voltage drop is specific to when charging by generator and then generator switched off.
Oh jea … Wintersun …
Can you get to the individual batteries to measure them individually now ?
To Compare the 4 Batteries …
Then you would have to measure the voltage on the battery again when your Multi is charging. There may be a contact problem and your battery may not get 57V at all. Because here only the Multi shows you the voltage … Only trust the values that you have measured yourself …
Sorry, nothing to measure them with 
But all seems good with them when charged by solar via the Victron Charge Controller
That would be a nice present for Christmas … 
Where there was the MK3 adapter … there might also be a measuring device …
It would also be interesting to know how the Mppt and the Multi are connected to the batteries. Is there a Lynx distributor or a busbar or perhaps something completely different?
Our setup is the minimum kit to get offgrid power.
9 x 330W Solar Panels going to:
SmartSolar MPPT 150/60-Tr Charge Controller going to:
4 x Victron 12V/165Ah GEL Deep Cycle Batteries going to:
Victron MultiPlus-II 3000VA – 48V, 35A Outlet 32A Transfer.
Backup Hyundai DHY8000SELR 5.00 KW 6.30 KVA Diesel Generator.
That’s it.
Maybe it’s time to add other toys so any recommendation is appreciated.
> That would be a nice present for Christmas
What should I ask for?
Thanks again for all your help so far 
Something like this because it has a DC Current Clamp !
Question again : Didi you use some Balancers ?
Only have the items listed so guess no balancers. What are they?