Low draw on full battery voltage drop issue?

[RVLiFe]

I've had my two 206Ah batteries in storage for about 4 months at 47%. Once a month, I would charge somewhere up to 90% and then drain them down to a little under 50% using a 55 Amp load. Today, I charged them to 100% at 14.6V and just ran my RV lights off of them for about 30 minutes. The lights drew only 3.2A and 41.54 Watts. Battery still had 99.3% of power based off of my SmartShunts reading but voltage of the parallel batteries is already down to 13.4V. Does this seem right? I've never seen the battery get to that low of voltage and still have 99% of the batteries capacity remaining. I would have expected it to get down to about 90% capacity before hitting that voltage. I'm going to continue running a small load for another day or two to see what happens. Has me concerned as to what a larger load would do to the batteries voltage. Is this typical or an indication of a faulty cell?

After an hour of use its even lower now.
This photo is of my Node-Red Dashboard

Edit: 1 hour 20 minutes in, voltage is down to 13.3V 99.1%
2 hours in, voltage is down to 13.25V 98.3%

 

[FilterGuy]

It is probably not an issue. That voltage is in the flat part of the charge curve where voltage is a very poor indicator of charge

 

[BentleyJ]

13.4V is 3.35V per cell and is a typical resting voltage for a fully charged battery with a light load. After a full charge cycle, our 48V batteries will fall to 53.6V in a couple of hours then down to 53.5V the next day with approx. 300mA standby load of the inverter and 2 BMS.

 

[Ampster]

After a full charge cycle, our 48V batteries will fall to 53.6V in a couple of hours then down to 53.5V the next day with approx. 300mA standby load of the inverter and 2 BMS.

I will just add that, it does not mean your battery has lost capacity. Some people describe that as surface charge.