Hmm you have 4 rows of 14 batteries each with each battery being 50v for a total of 700volts.
Or is each row of 14 batteries equal 50 volts.
Either way you can not just measure across each battery as you will have multiple earths and posatives comming togeather through your electronics.
You will have to measure in one of three ways.
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Starting with the earth you run one wire from between each battery and measure each wire with respect to ground. Placing a meter on all the wires and subtracting one voltage from the other.
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Same as the first but with only one volt meter switched between the wires.
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Individual volt meters across each battery and each electricaly isolated.
Perhaps you could share more info on this installation and what it does?
Daz