Solar installer saying it is because house has low voltage supply
Pure & absolute donkey pucks ! That shmuck is a fool, do not engage further!
I would not also completely doubt his work and have it rechecked by a real & credibly qualified person. Sorry but if someone bullshits like that, I would doubt everything else they say. That is an instant 3-Strikes your out !
Charger is capable of 60A Charge which is not bad and can service your two batteries.
You are describing a Standard Classic Case of overly aggressive charging parameters which sadly is ALL TOO COMMON ! We see this all the time, we suggest a proper profile (due to yrs of exp) and then get argued with about it by those that don;t know better. So one more time for a New Member.
1) a 48V system (legacy rating) is actually 51.2V nominal
2) LFP like ALL battery chemistries has TWO Voltage Ranges.
-- The Allowable Range is where the battery cells are safe where no harm more damage is incurred, this is from 2.500 to 3.650 volts per cell.
-- The Working Voltage Range which is where the Deliverable Amp Hours reside. This is from 3.000-3.400 Volts per cell. A VERY flat curve!
! Many companies like to push well into the Allowable range and that causes issues such as a runner cell hitting Hi Volt Disconnect which instantly stops charging on the battery pack. This can also reduce the entire bank capacity by becoming a "throttle" as the lowest cell rules the pack.
A proper 48V Charging Profile is below:
Absorb: 55.2V for 45 minutes (3.45vpc)
(some call this boost) * never actually runs the full 45mins because of EndAmps/Tailcurrent.
Equalize: OFF
Float 55.0V (3.437vpc)
MIn Volts: 42.2V (2.650vpc)
Max Volts: 57.2V (3.575vpc)
Rebulk Voltage: 51.2V (3.200vpc)
End Amps: #.#A (*1) (** Allows for full Saturation at set Float Voltage)
(*1): End Amps is calculated IE: (100AH X 0.05 = 5A or 280AH X 0.05 = 14A.
EndAmps = TailCurrent The term varies with companies, it is the same thing.
Coulumbic Efficiency / Battery Status Meter Efficiency for LFP = 99%.
This gets the bank charged to full with high amps (Constant Current - Constant Voltage) and then float (Constant Voltage - Variable Current) tops off so the cells are at 3.47Vpc.
* Do Not forget to adjust for Voltage Offsets between Actual Voltage @ Battery Terminal & at Solar Controller.
Very Special NOTE: Floating & Saturating to 3.437vpc, accounts for the Voltage Settling post Charge of any kind which actually brings the cells to just below 3.400Vpc.
One of my handy references for you to have handy, download &/OR print.