Volkswagen Golf 1999 Service Manual page 4291

Battery, charging
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Charging totally discharged
batteries
Batteries that have not been used for long
periods of time begin to self discharge (e.g.
vehicles in storage). Under these conditions,
the battery begins to sulfate and the surface
area of the battery plates hardens. A battery
is considered to be totally discharged if the
no load voltage is below 11.6 volts. No load
voltage, checking
On totally discharged batteries, the
electrolyte (sulfuric acid/water mixture) is
almost all water. When these batteries are
exposed to freezing temperatures,
permanent damage to the battery plates
(and housing) results.
If a totally discharged battery is charged
quickly ("quick charged" or "boost charged"),
only a surface charge is accepted (if at all).
The battery may even test OK immediately
after charging. However, in this case the
sulfating process continues inside the
battery. Once a battery begins to sulfate, it's
ability to further accept a routine charge
(from the Generator) and provide adequate
load and reserve performance will diminish
until the battery malfunctions.
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13/2/2005