Newbie - Charging and Maintaining AGMs for backup system - IP22

DIY
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1

Hi
Newbie here.
I currently have four 6V 210Ahr AGMs in a series / parallel circuit for 12V output. These batteries are about 5 years old, but have never had any load on them (which may be a bad thing). The batteries are feeding a 2,200 Pure Sine wave inverter to provide backup power for backup sump pump, fridge, and gas furnace blower.

I have been using a 12V 5amp “Battery Tender” but I think that has just been giving me a false sense of security. This weekend I used my car battery charger set for 12v - 15A - AGM and was able to get the battery bank up to 12.9v.
The 6v batteries are as follows 6.4, 6.3, 6.3, 6.5.

I am looking at the IP22 as a good choice to maintain the battery bank and I have some newbie questions.

  1. When discussing or designing an application does it matter that I am dealing with a bank of batteries versus a single battery? Assuming all the batteries making up the bank are in good working order.
  2. Is the IP22 a good choice for maintaining the battery bank? The batteries can go months without seeing a load.
  3. Should I cycle the power once a month on the IP22 so it can take a fresh look at the state of the bank? I could easily do this with home automation.
  4. Would the IP22 30Amp be an acceptable size for a 420Ahr battery Bank. Recovery time is not all that important, 24 hours would be fine.

Thanks for any help.