Porsche 928 ST1991 Owner's Manual page 97

Battery charging
Automotive batteries lose their efficiency
when not in use. The charge available in your
battery can be measured with a hydrometer.
We recommend that battery voltage be
tested by your Porsche dealer who has the
appropriate equipment. If the car is not dri-
ven for prolonged periods, the battery must
be charged at least every 6 weeks. A dis-
charged battery allows rapid formation of
sulfates, leading to premature deterioration
of the plates.
WARNING
• Charge battery in a well ventilated area.
Keep away from open flame or electrical
spark. Do not smoke. Hydrogen gas
generated by the battery is explosive.
• Electrolyte fluid that may spill during
charging should be washed off with a
solution of warm water and baking soda
to neutralize the acid.
• If you get electrolyte in your eyes or on
your skin, immediately rinse with cold
water for several minutes and call a doc-
tor.
• Never charge a frozen battery. It may
explode because of gas trapped in the
ice. Allow a frozen battery to thaw out
first.
• Never use a fast charger as a booster to
start the engine. This may seriously
damage the vehicle's electrical system
and the charger.
96
• Fast charging a battery is dangerous
and should only be attempted by a com-
petent mechanic with the proper equip-
ment.
Slow battery charging
WARNING
Heed all warnings and follow instructions
that come with your battery charger.
• Disconnect battery cables and remove
the battery.
• All vent caps should be open. If fluid level
is low, it should be topped up to the full
mark in each cell.
• Connect charger cables.
Charger cables must be connected POSI-
TIVE (+) to POSITIVE (+) and NEGATIVE (-)
to NEGATIVE (-).
• Do not connect or disconnect charger ca-
bles while charger is operating.
• Switch on charger.
• Normally, a battery should be charged at
no more than 10 percent of its rated
capacity. Rated capacity of the battery in
your vehicle is listed on the battery hous-
ing.
• After charging, turn off charger and dis-
connect charger cables. When the elec-
trolyte fluid has stopped "bubbling" in the
cells, close the vent caps.
• Tighten the vent caps and reinstall bat-
tery.