... I am going on a long trip to Alaska and I want to test these batteries to make sure they are still holding a total charge. ... Does anyone have any suggestions?
I'm normally a use it 'til you can't no more type of guy.
In this case...
If original, your battery bank is 6 years old. Has the bank ever been discharged to below 50% SOC? That reduces service life. Do you plan on dry camping often or using campgrounds?
Factors to me are reliability, peace of mind, and cost. You may avoid replacing batteries for some time, but they won't last forever. What is the cost of a bank of batteries when compared to the overall costs of the trip?
We did a really great trip out west last October. I had some ideas of expected cost, but I admit that I didn't do a detailed project estimate. When I totaled the fuel costs it was a bit of a surprise. Using the total miles traveled and an average mpg number showed that the actual fuel cost should have been expected, but I digress.
If the battery condition tests great, go for it. If at all in question the bank should probably be renewed.
vic