Lifeline Technical Manual

Document No. 6-0101 Rev. D Page 22 of 38
5.8 Temperature Considerations
The temperature of the battery has a significant impact on its performance and life capability.
Battery capacity is reduced significantly in cold temperatures. For example, a battery that
operates continuously at -18ºC (0º F.) will only provide about 60% of its normal room temperate
capacity. Appendix C provides a chart of capacity versus temperature at various discharge
rates.
Battery life is also affected by temperature. As a rule of thumb, the battery life decreases by
50% for every 10⁰C rise in temperature. Thus, a battery that lasts 6 years at 25⁰C will last 3
years at 35⁰C, 1.5 years at 45⁰C, and 0.75 years at 55⁰C.
It should be realized that the temperature of the battery itself and ambient temperature can be
vastly different. While ambient temperatures can change very quickly, battery temperature
change is much slower. This is due to the large thermal mass of the battery. It takes time for the
battery to absorb temperature and it takes time for the battery to relinquish temperature.
If the battery is exposed to cold climates, the state of charge should be kept at a maximum to
prevent freezing of the electrolyte. A fully charged battery will not freeze even under the coldest
weather conditions, but a discharged battery will freeze even when moderately cold. Table 6-2
gives the freezing point of electrolyte at various states of charge.
Frozen batteries are not capable of charging or discharging except at very low rates, and may
be permanently damaged by expansion of the electrolyte. If a battery becomes frozen, it should
be thawed by placing it at room temperature for at least 24 hours, and then charged in
accordance with Sections 5.4, 5.5 or 5.6 as applicable. However, if the battery container has
any evidence of cracking, the battery is no longer serviceable and should not be used.
Table 6-2. Electrolyte Freezing Point at Various Battery States of Charge
Battery
State of Charge (%)
Approximate Electrolyte
Freezing Temperature
100%
-70°C (-94°F)
75%
-47°C (-53°F)
50%
-25°C (-13°F)
25%
-13°C (9°F)
0%
-6°C (21°F)