Battery capacity and battery recharge times are all based on each cell having an electrolyte temperature of 25ºC (77ºF). Temperatures below the nominal 25ºC (77ºF) reduce the battery's effective capacity and lengthen the time to restore the battery to full charge. Temperatures above 25ºC (77ºF) will slightly increase capacity, but also will increase self-discharge and shorten battery life.

 

Major problems occur at temperature extremes. This is the range below 4ºC (40ºF) and above 38ºC (100ºF). Electrolyte in a fully charged battery has a freezing point of about -65ºC (-85ºF) but electrolyte in a fully discharged battery with low specific gravity has a much higher freezing point just below 0ºC (32ºF). A fully discharged battery, is endanger of freezing below 4ºC (40ºF) and should be charged immediately or un-repairable damage will result.

 

Lower Temperature – lower capacity, more heavily cycled.

Higher Temperature – higher capacity, more self-discharge and battery wear.



Effect of Temperature


Battery capacity and battery recharge times are all based on each cell having an electrolyte temperature of 25ºC (77ºF). Temperatures below the nominal 25ºC (77ºF) reduce the battery's effective capacity and lengthen the time to restore the battery to full charge. Temperatures above 25ºC (77ºF) will slightly increase capacity, but also will increase self-discharge and shorten battery life.


Major problems occur at temperature extremes. This is the range below 4ºC (40ºF) and above 38ºC (100ºF). The electrolyte in a fully charged battery has a freezing point of about -65ºC (-85ºF) but electrolyte in a fully discharged battery with low specific gravity has a much higher freezing point just below 0ºC (32ºF). A fully discharged battery is in danger of freezing below 4ºC (40ºF) and it should be charged immediately or un-repairable damage will result.

 

Lower Temperature – lower capacity, more heavily cycled.

Higher Temperature – higher capacity, more self-discharge and battery wear.


Cold Operating Temperatures


Cell temperatures below 4ºC (40ºF) have a high internal resistance during recharge. The cell voltage will climb rapidly and once above 2.35 VPC gassing commences. This causes excess water loss and plate corrosion. The voltage setting should be increased in colder ambient temperatures. If the voltage regulation of the charger is not increased the battery will not be recharged in 8 to 9 hours. The battery will more than likely be operated in a partially recharged condition. This increases the risk of battery sulfation which causes further recharging problems, greatly compounding the problem.


To summarize:


In cold operating temperatures:


1 - Understand battery capacity will be lower

2 -  Do not let the battery discharge to a specific gravity where freezing of the electrolyte can occur

3 - Increase voltage regulation settings and recharge times


Hot Operating Temperatures


In hot ambient operating temperatures, cells temperatures exceeding 43ºC (110ºF) should be avoided. A battery on charge will experience approximately a 10ºC rise in cell temperature in an ambient range of 35ºC (95ºF). Charging should be more closely monitored in temperatures >95ºF. Charging currents should be reduced or charging should be stopped until the battery is allowed to cool if 43ºC (110ºF)

 is exceed as very serious damage can occur at temperatures of 52ºC (125ºF).


Batteries on discharge will generate heat. This heat generation is moderate and not a problem during normal discharge conditions. However, when discharged at very high rates high ambient temperature conditions must be avoided. A high rate would be quickly draining the battery in 1-2 hours. The combination of high ambient temperatures above 35ºC (95ºF) and high discharges rates can cause serious battery damage. These high discharged rates can be avoided by using a larger capacity battery.

 

In hot operating temperatures:


1 - Don’t not let cell temperatures exceed 43ºC (110ºF)

2 - Let battery cool if 43ºC (110ºF) is reached

3 - Avoid very heavy loads to avoid rapid discharge rates.