Won't be able to test individually as it is a 12 volt tester. The "bank" would need to be tested (12 volts).
I agree; you need to test using the AH setting.
Remember the AH of the batteries with be the same as ONE 6 volt battery.
Connecting in series, the AH does not double, the voltage does.
When connecting in parallel, the AH doubles and the voltage does not.
To convert RC at 25 amps to AH:
To convert RC to Ampere-Hours at the 25 amp rate, multiply RC by .4167. More ampere-hours (or RC) are better in every case when looking for a deep cycle battery. Within the same battery footprint or industry group size, the battery with higher ampere hours (or RC) will tend to deliver longer cycle lives. This conversion method will allow you to convert and compare competitive data.
Using this calculation for your RC @25 number the AH for your bank is 220AH.
I would be curious to learn what the bank actually tests out as.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW