Big Rig Basics
Test for the Deep Cycle
Keep an eye on battery-cell water levels to keep voltage high longer
By John Baxter
Tim Ruth, president of Warehouse Battery Outlet, says truck batteries traditionally offered high CCA, or “cold cranking amps,” because starting the diesel was the primary load. But now that truckers shut down and run various accessories all night, deep cycling, where much of the battery’s stored power is taken out every night and replaced each day, is the battery’s biggest challenge.
Traditional batteries jam a large number of thin plates into each of the 6 cells that make up a 12-volt truck battery. This gives high amps for starting, but when the battery’s charge is pulled down a lot each night, the thin plates warp and bend and soon will short out. Putting on a larger alternator only makes matters worse.
Most trucks today need deep-cycle batteries with a lot of reserve capacity, which is rated at a low amperage draw typical of what cab accessories need when running. A battery with 200 hours of reserve capacity has fewer, thicker plates. It offers a little less CCA, but will last much longer with overnight shutdowns.
Ruth also suggests that when you operate in a no-idle situation to check water level frequently, as the water in the cells will evaporate quickly. Following find steps to do just that.
7. Smith found a bad cell, indicated by all the balls floating near the bottom of the hydrometer. Ruth said you can also check condition by measuring voltage with the engine off. A battery is dead at 12.1 volts, and fully charged at 12.6 volts.