question

Please check with the manufacturer if you can connect those LiFePO4 batteries in series. Most of the time, the series connection is not allowed for these batteries due to the safety features of the BMS.

However, you can run a 48V solar panel, if the VOC of the panels does not exceed 100V of the charge controller. You can calculate that from Victron's MPPT calculator portal.

If you are thinking of connecting those two in series, then individually charge them as a 12V battery bank. I have no idea what is going to happen in this situation. Maybe it's best to leave it for Rick and Morty to do. Although I am curious to find out if anyone has experimented it and wants to share their experience.

The manufacturer states the following:

Series or parallel connection When connecting batteries in series or parallel, make sure that each battery is within 500 mV (0.5 V). It is recommended to fully charge the batteries individually once a year to avoid imbalance. When charging Volthium batteries in series, it is best to use a multi-bank charger which charges each battery individually to ensure that the cells remain balanced.

In principle, I see this only being an issue if the charger shares a common ground. If each ground is isolated, I don't believe there will be an issue provided the charger works as intended. My main concern is that the MPPT will be choosing its output based on the voltage it sees at its charge output. Adding additional transformers downstream for charging batteries may cause issues if the batteries are not balanced, since the charge voltage will be fixed.

If series connections are allowed, you can use a Battery Balancer from Victron to balance individual batteries to keep it under the specified deviation, while the MPPT you have will charge both batteries connected in series at 24V.

Also, you can try reducing the charge Amps in the MPPT's Battery settings and start with 5 Amps of charging, and see if it does not trip the BMS to turn the battery off.

If it's still not charging, check the Voltage of the battery banks, and see if they are not above the Bulk Charging voltage of the charger. As the MPPT thinks it is fully charged and does not harvest any power.