A battery’s primary duty is to start the truck, but this task isn’t as simple as many would think. With diesel engines, cranking RPM is far more critical than with gas engine automobiles because of the way compression ignition behaves. Lose a few RPMs, and the air charge sacrifices more heat to the cylinder walls on the piston upstroke, preventing ignition.
This problem is compounded by injection system behavior, says Bruce Essig, business manager of the Odyssey program at Enersys. A slower cranking speed also means less injection pressure, and less chance of a start. Colder weather increases oil viscosity at cold start, compounding the problem even further in more severe winter climates.
“You want to make sure you have enough cold cranking amps (CCA),” says Gale Kimbrough, technical services manager of Interstate Batteries. “Most fleets use three or four batteries. Make sure you meet or exceed the truck engine OEM’s starting specs.” Going a little over can be useful because cabling and connections can deteriorate, says Kimbrough, who warns not to go overboard with high CCA ratings because that can shorten starter life.
“The battery is the heart of the electrical system,” Kimbrough says. And the toughest abuse for an alternator is bad batteries. Keep batteries working efficiently, and the alternator will live a lot longer because it will need to make far less power. That means not only maintaining cables and connections, but also specifying batteries that will live the way your particular fleet uses its vehicles, Kimbrough says.
Also look for a good warranty, and make sure the battery maker always has someone available who can answer questions, says Kimbrough, who also advises customers to check that the battery has not been on the shelf longer than three months.
With anti-idling regulations and fuel costs causing more trucks to shut down overnight, some truck batteries need to do more than supply a brief, high-current shot to start a truck.
“As the power plant shifts over to the electrical system, batteries become more important,” according to Optima batteries spokesperson Carie Wlos. “The battery pack will be counted on to provide more cycling capabilities and better recharge properties.”
That’s when reserve capacity comes into play, says Bruce Purkey, president of Purkey’s Fleet Electric. RC is the number of minutes a battery at 80 degrees can supply 25 amps before it reaches 10.5 volts from a full charge.
The basic issue is how much CCA and/or RC you can squeeze into a battery’s volume. The trucking world has settled on the Group 31 envelope, which is 13 inches long by 6.8 inches wide by 9.4 inches tall. High CCA batteries need more surface, so their plates, by necessity, must be thinner to fit. Thinner plates supply the amps for short periods, but “they have less ability to cycle,” Purkey says.
“It’s a common misconception that the more CCAs you have, the more power you’ll have for everything else,” says Jeff Coleman, director of OEM sales of automotive batteries for Deka. A high CCA battery that gives 700-900 cold cranking amps may give 400 relatively deep discharge cycles before it fails, Purkey says. A 1,000-amp CCA battery might give only half that, he says.
“A Group 31 high CCA battery can give as much as 1,100 CCA,” Essig says. “But if you need to deep-cycle it, the CCA number would have to drop to 800.”
Trucks with day cabs that use their batteries just for starting only need to worry about CCA, but trucks that have a bunk need dual-purpose batteries. Purkey says 180-200 RC is a good rating; four of those could provide 800 minutes at 25 amps.
When choosing hotel load, figure 11 amps DC for each 110-volt AC amp, and to remember there is also a 10-25 percent loss of power across an inverter, Kimbrough says.
AGM, or “absorbed glass mat” battery technology – where the acid is stored in fiberglass that acts like a sponge, so there is no free liquid electrolyte – also is worth considering, Purkey says. Enersys invented and patented this type of battery in the early 1970s, and now makes a high-performance version of it called the Odyssey that often will run for six years, Essig says.