Weather conditions

[skipsmith521]

Can someone help me to understand...

I have seen battery charts showing rating and referencing 80 degrees.

Does this mean that if the outside or battery temperature is say 40 degrees...your individual battery Volt reading and also pack charge will show a lower reading for say every 10 degrees below 80 degrees?

Am I understanding that correctly? Trying to understand how cold weather affects batteries and Volt readings...if any...

Skip

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[JohnnieB]

Lead-Acid cells (a battery is a group of two or more cells) generate electricity by a chemical reaction and the chemistry is more active at higher temperatures than it is at lower temperatures.

The net effect of a lower temperature is:
1. Less storage capacity.
2. Lower open circuit voltage.
3. Longer lifespan.
4. Charges slower.
5. Specific Gravity of the electrolyte is lower.

The net effect of higher temperature is just the opposite.

In the metric universe, 25°C (77°F) is the temperature batteries are rated at and in the non-metric universe, 80°F (26.67°C) is used.

Storage capacity changes roughly 5% per 10°F change in temperature. Increasing above 80°F and decreasing blow 80°F.

Open circuit voltage changes roughly 0.004V per 10°F in temperature.
Increasing above 80°F and decreasing blow 80°F.

Lifespan decreases roughly 1.67% for each 10°F above 80°F and increases roughly 4.35% for each 10°F below 80°F.

Unless you are using a temperature compensated charger, the battery charge tomes will be shorter above 80°F and longer below 80°F.

If the battery charger is temperature compensated, the on-charge voltage will be higher when temperature is below 80°F to offset the slower chemical reaction.

Add 0.004 to your hydrometer read for each 10°F above 80°F and subtract 0.004 for each 10°F below 80°F.


BTW: A battery has a huge thermal mass and its internal temperature can lag air temperature by hours, so use electrolyte temperature rather than air temperature.