Victron energy BMV-600S Manuel page 11

If the Peukert exponent is not provided with your battery, you can
calculate it by using other specifications which should be provided with
your battery.
The Peukert equation is stated below:
n
where the Peukert exponent, n =
Cp I t
= ⋅
The battery specifications needed for calculation of the Peukert
exponent, are the rated battery capacity (usually the 20 h discharge
1
rate ) and for example a 5 h discharge rate
example of how to define the Peukert exponent using these two
specifications.
C
=
5 h rating
5 h
t 5
=
1
I
=
1
Peukert exponent, n
=
When no ratings are given at all, you can measure your battery using
a 'constant load bank'. In this way a second rating can be obtained,
together with the 20 h rating which represents the rated battery
capacity in most cases. This second rating can be determined by
discharging a fully charged battery with a constant current; until the
battery reaches 1.75 V per cell (which is 10.5 V for a 12 V battery or
21 V for a 24 V battery).
1
Please note that the rated battery capacity can also be defined as the 10h or even 5h discharge rate.
2
The 5h discharge rate in this example is just arbitrary. Make sure that besides the C20 rating (low discharge current) you choose a second rating
with a substantially higher discharge current.
75 Ah
20 h rating,
h
75 Ah
15 A
=
5 h
log 20 log 5
−
=
1 . 2 6 1 . 2 6 1 . 2 6 1 . 2 6
log 15 log 5
−
log t log t
−
2 1
log I log I
−
1 2
2
. See below for an
C 100 Ah (rated capacity)
=
20 h
t 20 h
=
2
100 Ah
I 5 A
= =
2
20 h
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