After nearly 40 years of experience in the industry,I have come to a conclusion; you can do all the magic testing, check the water weight, check the voltages, change a cell, dance on 1 foot during a full moon, dazel your customer w/ BS. The only thing that I found that works is:
1) if a cell has to be replaced in an older battery, take it to the glue factory. The other cells are sure to follow suit.
2) if the battery can do 5 hours of daily usage on a single charge at least 2X keep it.
Remember the newer trucks are voltage sensitive, and a electronic repair is going to equate to a battery replacement any way.