Charge Status - Volvo FM Handbook

550 Maintenance

Charge status

It is useful to know how discharged a battery is before
it is charged, to be able to charge it in the best manner.
The ambient temperature plays a part in both the
charging ability and capacity, not until at +25 °C does
the battery give 100 % of its capacity. The battery
cannot be charged especially well below 0 °C, see
table.
The batteries must not be left uncharged. Every third
to fifth week, even a "charged" battery needs a
maintenance charge, due to self-discharge and possible
small consumers <40mA (clocks, tachograph etc.) if
the vehicle does not have a main switch. If there is a
main switch and a properly connected solution, one
can stretch to five weeks between maintenance
charging.
Temperature
Capacity 20 h (Ah)
Charge acceptance (A)
An alternator can never charge the battery to 100%; in
favourable circumstances a maximum level of 90%
can be achieved. Complete recharging can only be
done with a battery charger over a long period of time
(1-2 days). Increased power demand from the
alternator and battery may result in the battery being
discharged. The easiest way to check the charge is
with a voltmeter, but an aerometer (specific gravity
gauge) together with a voltmeter gives a more correct
result. The diagram below shows the rest potential and
state of charge compared with the specific gravity of
the acid.
-18ºC 0ºC
50% 85%
6% 25%
+25ºC
100%
100%