Volvo XC90 Owner's Manual page 591

Support battery
Vehicles with the Start/Stop function are equip-
ped with two 12-volt batteries – a heavy-duty
start battery and a support battery that provides
extra current during the function's start
sequence.
The support battery is located in a box next to the spring
strut in the engine compartment.
NOTE
• The higher the current consumption in
the vehicle, the more the alternator has to
work and the batteries have to be
charged = increased fuel consumption.
• When the starter battery capacity has
dropped below the lowest permissible
level, the Start/Stop function is disen-
gaged.
When the Start/Stop function is temporarily
reduced due to high current consumption:
• The engine will auto-start, even if the driver
does not lift their foot from the brake pedal.
The support battery does not normally require
more service than the start battery. If you have
any questions or concerns, consult a workshop ‒
an authorized Volvo workshop is recommended.
CAUTION
If the following is not observed, the Start/
Stop function may temporarily stop working
after connection of an external starter battery
or battery charger:
• The negative battery terminal of the vehi-
cle's starter battery must never be used
to connect an external starter battery or
battery charger – only the vehicle's neg-
ative charging point should be used as
a grounding point.
MAINTENANCE AND SERVICE
NOTE
If the starter battery has been discharged to
the extent that the vehicle does not have nor-
mal electrical functions and the engine must
then be jump-started with an external battery
or a battery charger, the Start/Stop function
may remain activated. If the Start/Stop func-
tion shortly thereafter auto-stops the engine,
there is a huge risk that auto-start of the
engine will fail due to insufficient battery
capacity since the battery had not had time to
recharge.
If the vehicle has been jump-started or if
there has not been enough time for the bat-
tery to be charged with a battery charger, the
Start/Stop function should be temporarily
deactivated until the battery has been
recharged by the vehicle. At an ambient tem-
perature of about +15°C (about 60°F), the
battery must be charged by the vehicle for at
least one hour. At lower ambient tempera-
tures, the charging time can increase to
3-4 hours. It is advisable to charge the battery
with an external battery charger.
Specifications for support battery
Type
Voltage (V)
AGM
12
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589