Low voltage Disconnect

Usually suggest around 11.5 (12 volt bank) or 46.0 volts as a LVCO level for "lightly loaded" set-point. And 10.5/42.0 volts as a cutoff for heavier loads (such as during starting a well pump.

You seeing ~50 volts (12.5 volts) as a resting voltage on a battery bank (not under charge) is usually indicative or a "good bank" at something like ~70% or so state of charge.

If this was the resting voltage of a bank that just came off charging and was supposed to be ~100% SoC--I would guess that this is not great but a sign of possible sulfation of a lead acid bank. And the next step would be to try an do some EQ charging (charging at ~60-62 Volts--Try for 2.5% to 5% rate of EQ charging current) and charge until the specific gravity of each cell stops rising ("new" full charge SG value)--And stop EQ if bank is overheating (and continue EQ the next day). Industrial batteries such as Rolls seem like they can take a few cycles of "hard" EQ over a couple days/several weeks of normal cycling and a (for example) weekly "hard" EQ to bring back up the "full charge" SG voltage.

If you cannot get the SG to rise and/or your battery bank cannot support the microwave loads today--Then the bank may be on its (for you) last legs of service life (if a bank cannot do what you need anymore--Then it has lost it usefulness for you).

Of course, there are the usual checks for bad/loose wiring... Look for any warm/hot connections/cables under heavy current (be careful not to burn your hand on a hot connection). What is the Bank voltage and voltage at the AC inverter DC input terminals under load/around when the shutdown occurs. Is the inverter shutting down at ~42.0 volts (normal LVCO voltage from factory)? Is there a large drop from Battery Terminals to inverter DC terminals? Are any electrical connections hot (dirty/loose/corroded connections/wiring)? Check for excessive voltage drop with meter set to (for example) 2.000 V max scale and when under heavier load or charging, see if you can find a terminal (or cable) with excessive voltage drop compared to rest of connections/cables.

Also check the terminal of each battery (cell) under charge/discharge. Look for batteries that are "different". A high voltage during charging may indicate a failing battery. A low voltage during discharging may indicated a failing battery. At resting, a low battery voltage may indicated a shorted cell, etc...

You have two parallel strings? Each string taking/supplying its share of total current (i.e, not one string with 30 amps and the other with 3 amps)?

You have a hydrometer and DC current clamp DMM?

If you do not have a current clamp meter--I have take voltage readings on cable voltage drop (under load/charging) on two identical length cables in two strings and use the cable like a shunt resistor. If one cable reads 0.020 volt drop and the other 0.010 volt drop--Then the cable with the smaller drop is probably carrying ~1/10th the current (the days when there were no "cheap" DC current clamp meters and I was "too cheap" to by the expensive meter).

Age of bank? Have you gotten your 3-5 years or upwards of 7 years (OK to pretty good) service life for low cost Golf Cart batteries from your bank?

-Bill