**Peukert in brief**

The usual form of Peukert's equation is T=C/I^{n}

Where:

T = time in hours

C = the Peukert capacity of the battery (ie at the 1 amp discharge rate)

I = the discharge current

n = Peukert's exponent.

This equation will only work on batteries that are specified at the "Peukert Capacity" ie the 1 amp discharge rate. They **very** rarely are.

Batteries are usually specified at an "hour" rate, for instance 100Ahrs at 20 hours. Or 90Ahrs at 10 hours etc.

If your batteries are specified in such a way (and they nearly always are) then the equation must be modified to take this into account.

The modifed equation is T=C(C/R)^{n-1}/I^{n} or T=R(C/R)^{n}/I^{n}

Where:

T = time in hours

C = the specified capacity of the battery (at the specified hour rating)

I = the discharge current

n = Peukert's exponent

R = the hour rating (ie 20 hours, or 10 hours etc)

Alternatively, do this:

R(C/R)^{n} = the "Peukert Capacity".

So in the case of a battery specified as being 100Ahrs@20 hours with a Peukert's exponent of 1.25 we get:

20(100/20)^{1.25} = 149.5Ahrs. This is the "peukert capacity". ie the capacity of the battery when discharged at 1 amp.

If you use this figure as the capacity of the battery then the usual Peukert's equation of T=C/I^{n} can be used.

There is a slightly different Peukert calculator here that operates by adjusting the specified battery capacity to the "Peukert Capacity" then showing run times calculated using the usual T=C/I^{n}

This spreadsheet is slightly different from the one here as the first one calculates the "Peukert capacity" then