Best Recharge Volt

You need to review the manual/specifications for your battery bank...

For Flooded Cell Lead Acid batteries that are designed for deep cycling... Keeping them in "float" (basically) > 12.8 volts (or 51.2 VDC @ ~77F/25C resting voltage) to upwards of 13.4 to 13.6 volts (ref 12 volt battery bank or 53.6 to 54.4 volts). Old/failing FLA batteries (and forklift/traction batteries) tend to use more float current.

You are looking for two things--You want to account for "self discharge" (typically <1% rate of self discharge) and you want to "instantaneous" battery bus voltage to keep above >~51.2 "valley" voltage)...

What do I mean by this? A single phase AC inverter draws a (sine squared) 120 Hz (60 Hz AC) pulse wave from while operating... More or less at 120/240 VAC sine wave maximum peak voltage, inverter draws max current from battery bus. And at the "zero crossing" of the AC sine wave (near zero battery bus current).

If you had your "float voltage" at 12.8 volts (example) when AC inverter is running, the battery bus voltage may dip by 0.3 volt (picking number out of the air) or the "batteries see" 12.5 to 12.8 volts... Or you are "micro cycling" your battery bank by 120 HZ (AC inverter output power).

So, as an example, if you set "float" >12.8+0.3 volts or 13.1 VDC float--then the batteries will not be "micro cycled/discharge" while floating.

Assuming deep cycle FLA batteries--There have been discussions that they should be "cycled" from 100% to 75% (or less) SoC once a month... Both to show that everything is functional--And that "cycling" FLA deep cycle batteries is good for them (mixing electrolyte, shedding inactive plate materials, etc.)...

If you have "float service" FLA batteries (and AGM?), just keeping them at Float (per factory specs) is the way to go...

Long term, monitor water usage... FLA batteries do use water (say needing topped off every 2-6 months) if charging voltage(s) are set correctly. No Water usage, perhaps under charging. Too much water usage, may be "cooking" the batteries (note: there are different battery plate additives that can reduce water usage--The above numbers are "generic"--Your specific cells may be different).

When to EQ... That is always an interesting discussion... "Tall cased" batteries generally are EQ'ed more often to mix the electrolite (once a month?). Also EQ if Cell to Cell SG varies by >0.030 SG units (EQ just enough to bring up low cells to match/they don't increase SG from reading to reading--every 30-60 minutes). Watch battery temperatures--Is possible after many hours at 2.5-5% rate of EQ charge to overheat battery bank (heat not good for FLA batteries).

Lastly, for FLA batteries that are kept on "Float Charging"... If you see float charging current approaching 2%+ rate of charge (522 AH => 10.4+ Amps) the battery bank is "end of life" (or float voltage is too high) and the batteries can overheat and fail.

You are looking for "differences" between cells/batteries in your bank. One battery with Higher or Lower voltage (or SG) than its neighbors--Needs to be looked at (check for clean/tight wiring connections, corrective EQ, etc.). Seeing Float Charge current increasing (less than 1% to over 1%, etc.), battery temperatures rising, too much or too little water usage, etc...

Keep a log (SG, SG for pilot cell, cell/battery voltages resting/under discharge/under charging, etc.)--Watch for changes over time.

-Bill