When I do a field battery test, I count the number of cells and write them down on a piece of paper in a column. I remove every plastic jumper cover. This is so when I test with a meter, that i will be sure to break through any corrosion to get to the metal. I make three more columns on the paper, which are: state of charge (V), loaded volts (V), and specific gravity. I start with measuring latent voltage across the cell to which the positive cable is connected (cell 1) and work my way along the jumper path towards the negative cable. I take SG readings in the same fashion, noting each reading in the column. Then I take loaded voltage readings by deadheading the lift until the voltage reading stabilises, then recording that voltage.

I prefer a fully charged and rested battery to measure just under 2.2V, SG to read 1.260/1.270, and loaded voltage to drop to about 2 or just under 2V. An older or tired battery can have slightly lower readings, but what you want to watch for is consistency across all cells. If you have a few bad apples in an otherwise strong battery, by all means go ahead and replace them. However, if you cant get even the good cells up past 1.9V after a charge and it drops to like 1.6 under load, any new cells you put in it will just burn up; time to retire the whole assembly.

A more advanced method of testing a battery involves use of an electronic load tester that will take the battery through a whole cycle and tell you how it performs through that cycle. this will tell you whether you have a good 6 hr battery or if you can only get 4 hrs or less out of a full charge. These testers are extremely expensive and only practical to buy if you are in the battery business.