Thanks for the informative reply.
I had tried to upload a spreadsheet with our SG readings in it, but Yahoo was acting up. I tried again in this reply, but it won't upload the attachment. The average SG was 1.226 with a low cell of 1.215 and a high cell of 1.445.
I think I'm probably going to have to remove the pair that has the low SG reading battery in it from the wiring. I won't pull the batteries out of the box since they make for a nice tight fit.
The batteries were new in August of 2016, so they're less than two years old. The next time I replace the batteries, I'm going to replace the charger as well. Having a charger that will equalize the batteries, and has adjustable charging voltages, only makes sense. The cost of the battery charger is about equal to new batteries so it's an investment, but we plan to keep the boat a few more years.
I'm still wondering when you replace the entire suite of batteries? The lower limit of the "fair" range on my SG tester is 1.210 so I guess that's the trigger for replacement?
Replacing the charger with a charger/inverter, the inverter will be a boon for AC for the microwave and outlets (i.e. popcorn and computer charging anytime you want to!). I don't expect my third Xantrex Prosine 1800 watt inverter to last any longer than the first two did (replaced sequentially under a two year warranty).