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Battery Charger
Battery manufacturers typically recommend that you never discharge a deep-cycle battery
below a certain percentage of its capacity. Usually 50% to 80% is recommended. The V
value determines this (see section 8.1.2 )
4.4.1
State of charge
State of charge, or conversely, the depth of discharge can be determined by measuring the
voltage and/or the specific gravity of the acid with a hydrometer. This will not tell you how
good (capacity in Ah) the battery condition is. Only a sustained load test can do that.
Voltage on a fully charged battery will read 2.12 V to 2.15 V per cell. At 50%, the reading will
be 2.03 VpC (Volts per Cell), and at 0% the reading will be 1.75 VpC or less.
Specific gravity will be about 1.265 for a fully charged cell, and 1.13 or less for a totally
discharged cell. This can vary with battery types and brands somewhat. When you buy new
batteries you should charge them up and let them sit for a while, then take a reference
measurement.
Many batteries are sealed, and hydrometer readings can not be taken. Then you must rely on
voltage. Hydrometer readings may not tell the whole story, as it takes a while for the acid to
get mixed up in wet cells. If measured right after charging, you might see 1.27 at the top of
the cell, even though it is much less at the bottom. This does not apply to gelled or absorbed
glass mat (AGM) batteries (see section 4.7.2 ).
4.4.2
False capacity
A battery can meet the voltage tests for being at full charge, yet be much lower than it's
original capacity. If plates are damaged, sulfated, or partially gone from long use, the battery
may give the appearance of being fully charged, but in reality acts like a battery of much
smaller size. This same thing can occur in gelled cells if they are overcharged and gaps or
bubbles occur in the gel. What is left of the plates may be fully functional, but with only 20%
of the plates left.
Batteries usually go bad for other reasons before reaching this point, but it is something to be
aware of if your batteries seem to test OK but lack capacity and go dead very quickly under
load.
4.5
Temperature
Battery life and battery capacity are affected by temperature. Batteries perform best in
moderate temperatures. Battery capacity is reduced as temperature goes down, and
increased as temperature goes up. (This is why a car battery dies on a cold winter morning,
even though it worked fine the previous afternoon). If the batteries are installed in an
unheated part of a building, the reduced capacity has to be taken into account when sizing
the system batteries. The standard rating for batteries is at room temperature: 25
77
drops to 50%.
Capacity is increased at higher temperatures; At 50
higher. Even though battery capacity at high temperatures is higher, battery life is shortened.
Battery capacity is reduced by 50% at -27
life is reduced at higher temperatures - for every 10
This holds true for any type of lead-acid battery, whether sealed, gelled, AGM, industrial, etc.
The battery charging voltage also changes with temperature. It will vary from about 2.74 V per
cell at -40
8.1.4 ) on your battery charger must always be enabled, except for testing, maintenance, etc.
Bosch Security Systems B.V.
o
F). At freezing, capacity is reduced by 20%. At approximately -27
o
C to 2.3 V per cell at 50
Installation and Operation manual
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C, the battery capacity will be about 12%
o
C, but battery life increases by about 60%. Battery
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C above 25
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C. This is why temperature compensation (see section
Planning information | en
final
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C (about
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C, battery capacity
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C, battery life is cut in half.
180110011Aa | V1.1 | 2011.05
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