The capacity of a SLA battery is the
amount of electrical energy which can be obtained from a fully charged
cell. The capacity is expressed in ampere hours. The capacity
is dependent upon the discharge current, the temperature during the
discharge, the final cut-off voltage and the batteries general history
(storage temperature, charge, maintenance, etc.).
Whenever possible, store batteries in a clean, cool and dry place
so that it is not effected by sources of radiant heat such as sunshine,
heating units, radiators or steam pipes. The recommended storage
temperature and humidity levels are as follows:
between 32 and 104 degrees Fahrenheit (0 to 40C).
Storage Humidity should
be as low as possible.
Battery storage should
be avoided where temperatures can exceed 104F.
The temperature limits for
SLA batteries in operation are as follows:
5F to 122F (-15C to 50C).
Discharging: -4F to 140F
(-20 to 60C).
The ideal operating
temperature for SLA batteries is approximately 68F to 77F (20C to
25C). Operation at temperatures below -4F could result in physical
damage. When operating and charging at temperatures above 140F
results in accelerated drying of the electrolyte. Thermal runaway
and severe swelling may occur.
Remember that extreme temperatures shorten battery life.
Due to the chemical components of SLA
batteries, a reaction takes place in storage called Self Discharge, which
is a slow drain of a batteries capacity and is sometimes referred to as
Shelf Life. At room temperatures, the self discharge rate is about
3% of rated capacity per month. This low self discharge rate and the
batteries excellent charging characteristics permit storage for up to one
year without loss of efficiency or performance.
SLA batteries require a Top Charge with a
given time frame while being stored. The Top Charge replenishes the
capacity that was lost to the battery while in storage. After long
term storage, all batteries deliver less than the rated capacity.
Full capacity will be obtained through several discharge/charge
cycles. For longest life, batteries should be fully charged before
going into storage. Brief periods of high temperatures (a few days)
will have no effect on storage times. However, periods of one month
or more at temperatures higher than 78F will require an increase in the
frequency of Top Charging.
recommended Top Charging Intervals:
32 F or
32 F to
78 F to
Top Charging Recommendations For SLA Batteries.
It is important to charge SLA batteries with a well matched charger.
Because the capacity or life of batteries is influenced by ambient
temperatures, charging voltage and other parameters, it is important to
use a charger matched to the battery and its application.
It is recommended that the charge
voltage be adjusted to compensate for the battery temperature.
This may be done by detecting the ambient temperature near the battery
instead of the actual battery.
The reasons for temperature compensation of the charging voltage are:
To prevent thermal runaway of the
batteries when they are used in high temperature conditions.
Sufficient charging when the
batteries are used in low temperature conditions.
Temperature compensation of the
charging voltage can prolong the trickle or float life or batteries as
Approximately 5% compared with no
compensation at 86F (30C).
Approximately 10% compared with no
compensation at 95F (35C).
Approximately 15% compared with no
compensation at 104F (40C).
When the batteries are used in low
temperature conditions, temperature compensation of the charging voltage
does not affect the trickle or float life of batteries. The
benefit then of temperature compensation is to keep the trickle or float
charging current almost the same as it would be at 77F (25C), even
though the temperature around the batteries varies.
In summary, batteries should be charged at:
An ambient temperature within the
range of 32F to 104F (0C to 40C).
The most effective charging range is
41F to 95F (5C to 35C).
Charging temperatures below 32F (0C)
or over 104F (40C) is not recommended, as the batteries might be
deformed by heat or not charged enough.