A Group 31 battery (surprised it isn't listed in the table above, maybe close to a G34) will fit into most battery compartments whether they originally came with G24, 27s or whatever. Whether in flooded lead acid (FLA) or AGM type they provide about 100 amp hours of capacity.
Sams or Costco is a good source for FLAs which can't be shipped. Amazon has shippable G31s from Renogy or WindyNation for about $200 each. Read up on the pluses and minuses of each type and decide.
I would definitely replace both at the same time.
David
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