Dear friend. I have an interesting problem ?
I have watched many boat lithium battery upgrades online (YT) all seems to go quite well 
. I had two lead acid batteries in my 5 battery bank began to gas quite badly. I decided to not only replace the batteries but also to take the opportunity to upgrade all to Lithium. There was little time to plan as we were in the process of moving marinas. After having the new batteries 
installed (Victron superpac 100ah 12v) we also upgraded our shunt to a victron smart shunt, also a Cerbo GX with touchscreen to monitor our system. We also have installed an Orion GX DC to DC controller. We have both solar panels and a wind generator topping up the batteries. Our battries are connected to a EDECOA 3500w inverter for our AC power loads. Our system is set to 14.2 V for a 100% State Of Charge.
My Question: When we have 100% State Of Charge (SOC) as we use a load say a kettle as the SOC goes down the voltage also seem to decrease e.g if the SOC goes down to 97% the voltage drops to 13.8 volts. If we disconnect the solar and wind (and shore power) this would mean :-
Battery … volts …
100 %. 14.2
90 %. 12.78
80 %. 11.36
70 %. 9.94
60 %. 8.52
50 %. 7.1
My understanding is you could set a lithium battery to 10% or 20% floor, but at this rate the batteries will not run any loads after 70%-80% what have i done wrong or do I need a victron inverter to fix the problem.
Only one 100Ah SuperPack is way to small for your system!
That battery can only deliver around 50A continuously and 100A peak for 10s.
That’s 600W continuously or 1200W peak.
14.2V is the charging voltage the idle voltage of a fully charged LiFePO4 battery is around 13.3V.
So a voltage drop under load is totally normal.
The amount of the drop is depending on the load, with a smaller load the drop is smaller.
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Sorry I thought I mentioned I have 4 x 100 ah batteries therefore, 400 ah total. So the drop in voltage is normal ?