Some data towards indication of
State of Charge (SOC) from cell voltage


Taking the information we have already gathered during the baseline battery tests, we can graph the relationship between voltage and SOC under a 70 amp load for some randomly selected batteries.

70 amp discharge to voltage study chart

For this graph, we use actual achieved capacity rather than rated capacity.

Notice that the curve of the graph of cell #74 matches the other 4 cells fairly closely but .02 volts lower. To check this anomaly, we graphed cells #73 and #75. Since their graphs match the other cells, it is unlikely there was a change in test equipment. Cell #74 test temperature and actual capacity is also within the range displayed by the other cells.

Out of curiosity, we add cell #77. This cell was one of the ones that charged in an aberrant fashion. Hitting 4.2 volts after only 50 amp-hrs rather than the 60 amp-hrs that was the norm for 90% of the batteries. #77 and #74 match fairly closely. Why do they both sag more under load than other batteries?


70 amp discharge to voltage study chart with #77

The Excel file can be downloaded by clicking the link below.

Zipped Microsoft Excel file with data and charts for 70 amp discharge to voltage study.



Establishing a baseline
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