Victron energy BMV-700 Anleitung Seite 12

2.2 Synchronizing the BMV
For a reliable readout, the state of charge as displayed by the battery
monitor has to be synchronized regularly with the true state of charge of
the battery. This is accomplished by fully charging the battery.
In case of a 12V battery, the BMV resets to 'fully charged' when the
following 'charged parameters' are met: the voltage exceeds 13.2V and
simultaneously the (tail-) charge current is less than 4.0% of the total
battery capacity (e.g. 8A for a 200Ah battery) during 3 minutes.
The BMV can also be synchronized (i.e. set to 'battery fully charged')
manually if required. This can be achieved in normal operating mode by
holding the + and – buttons simultaneously for 3 seconds, or in setup
mode by using the SYNC option (see section 4.2.1, setting number 10).
By default, the BMV is configured to start-up in a synchronized state and
will indicate a state-of-charge of 100%. This behaviour can be changed:
see section 4.2.1, setting number 70.
If the BMV does not synchronize automatically, the charged voltage, tail
current, and/or charged time may need adjustment. When the voltage
supply to the BMV has been interrupted, the battery monitor must be
resynchronized before it can operate correctly.
After having synchronized for the first time (automatically or manually),
the BMV keeps track of the number of automatic synchronizations:see
section 4.3, history item SYNCHRONIZATIONS.
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