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Re: understand 12v electrical
So far you've only confirmed that the batteries an dbattery monitor have different points of view. There's no reason to think the batteries would need to go back, although any battery dealer should have a load tester available to cycle and test the batteries and confirm their actual capacity. (Thousand-dollar plus computerized internal resistance testers, not just the old carbon pile load tests.)
I'd suggest you have two ways to go: Take the batteries in for testing, heavy grunt work and the risk of acid spilling and eating your cloths or something in the car (truck?).
Or, get a couple of old automobile high beams or a similar simple resistive load, and do your own real-time load tests on the batteries. With a typical 55W auto highbeam headlight (often free from the dumpster since folks tend to burn out the low beam first in dual-beam bulbs) you consume roughly (55/14.4) 3.8 amps per hour, so one of those bulbs should burn for about 26 hours to consume a real 100 amps from a battery bank. With a couple of multimeters you can confirm the amperage it is pulling and the voltage left in the battery, and you are close neough to the "nominal" 20-hour rate so thosefigures should still apply. This also gives your battery monitor a reality check versus the meters.
If the date code on the batteries (usually embossed or stamped near the top but hidden under the edge of the big label) in within the last 90 days, the odds are there's noting wrong with the batteries unless one is grossly defective.