# question

## C20 calculation with Peukert

Hi all mathemeticians

In the BMV manual p. 30 some details are given about Peukert's formula, but no way to estimate the C20 capacity as asked in the manual.

e.g my TYS batteries are announced with C10=1260Ah and C120=1740Ah The calculator gives n=1.15 but the C20 cell is gray

if C20=I^1.15 * 20, and I=C20/20 then C20=(C20/20)^1.15*20 and C20^0.15=20^0.15: the snake bites its tail!

Where am I wrong?

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Guy Stewart (Victron Community Manager) answered ·

It isn't necessarily linear, and you will only get the right answer by talking to the battery manufacture or doing a C20 discharge test yourself.

While it might not satisfy the mathematician, practically, using the C10 figure is probably the safe bet, you will have a bit more available capacity, and less likely to be caught short.

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