The 'C' rating is derived from manufacturers testing their batteries at varying loads and comparing the voltage drop. If a 5000mAh cell is at 4.2V, (under no load), and if under a load of 200A it drops to 3.9V, some people may say that 3.9V is still an acceptable level, and therefore it has a continuous 'C' rating of 40C. However, someone else may say that for continuous, a cell should hold 4.1V/cell, in which case the same Lipo would not be 40C, and would infact take, let's say, 150A. This means a 'C' rating of 30C.
There is no standard way of testing cells, and no overall concensus over what an 'acceptable' voltage drop is.
This is why some cells have a 40C discharge rating, yet seem to be outdone by cells that have a 30 or 35C discharge rating. One cell manufacturer is probably being a little optomistic, and the other perhaps a little conservative.
This is why I maintain that manufacturers of Flight cells (Flightpower, Thunderpower, Hyperion etc) produce more accurate ratings than those in the car fraternity (LRP/Nosram, etc).
Also ratings like '40C' are a little too round. I think 38.5C is probably more accurate for some, and there is some over optomistic rounding going on.
Well, that was long.
Oh, on topic again, the GM lipos seem very good, and probably better than the LRP/Nosram 40C batteries. They just seem to have more punch.
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