As mentioned earlier, available battery energy decreases as temperature drops. A fully charged battery at 80°F has 100 percent of its potential energy. The same battery at 32°F has only 83 percent of that energy available. At 0°F, battery power has dropped to 61 percent, and that decreases to a mere 10 percent at 230°F. Also, as temperature drops the amount of mechanical energy required to crank an engine is much greater, so much attention should be paid to the cranking circuit in cold weather.
When winterizing batteries during PMIs, disconnect battery cables and load test each battery individually at one-half the CCA rating for 15 seconds. For a battery rated at 900 CCA, carbon pile B load test at 450 amps for 15 seconds. The voltage should not drop below 9.6 volts during the test when performed at 70°F. When the test is performed at 0°F the voltage should not drop below 8.5 volts. Ambient temperature must always be taken into account when performing any battery tests.
Because it is important to keep batteries warm to optimize performance in cold weather, many trucks are equipped with battery heaters. Various styles are available. The most common are the blanket type and the plate type. The plate-type battery heater is placed either under or between the batteries. Blanket-type heaters come in a variety of lengths and wattages and usually incorporate their own insulation.
If you suspect a battery is frozen do not attempt to heat it rapidly. Trickle charge and observe for charge response.