Uptime and utilization are everything, so you don't want a truck sitting on the shop floor during basic battery maintenance. Most fleets pull the batteries at the first sign of trouble and replace them with fresh batteries to get the truck moving again, planning to deal with the bad batteries later.

But what killed the batteries in the first place?

If there's a problem with the truck's electrical system, simply replacing the bad batteries with fresh ones may consign those to the scrap bin, too.

Most batteries don't require much in the way of maintenance anymore. Inspect the case for damage, clean the terminals and you're good to go. But batteries do fail, and a single weak or damaged cell can take down a group of batteries. Electrical current, like water, flows to the lowest point - in this case, the cell with the lowest charge. So even with all systems shut off, current will still flow from good batteries to the bad one because the cells are connected. The first step is to identify the problem battery cell.

"You have to disconnect all the batteries in the group and test them individually," says Gale Kimbrough, engineering and technical services manager at Interstate Battery. "Today's conductivity testers can test a pack of four batteries in a group, but they may not isolate the bad one. The testers can also be influenced by corrosion on the terminal connectors causing small voltage drops."

If you can determine which battery is faulty, remove it and find out why it failed.

"Generally only one of the batteries in the pack is bad; the rest are likely discharged due to the bad battery," says Bruce Purkey of Pur key's Fleet Electric. "Recharging the good batteries and putting them back into service is a huge savings to fleets, as it helps them maximize their return on investment in these batteries."

If no battery stands out from the rest, perhaps the problem lies elsewhere, such as in the charging system, or a short or current draw somewhere there shouldn't be. That pushes the problem somewhere upstream of the batteries, out of the sphere of battery maintenance, yet the problems are intimately related.

Discharging while idle

Parasitic loads are created by onboard electronics, such as communications and instrumentation systems.

"If the engine is inactive for a long enough time, parasitic loads will drain the battery to discharge, at which point they are unable to maintain a voltage that is high enough for proper operation of electronic equipment," says Kalyan Jana, development support manager for specialty markets at EnerSys, makers of Odyssey batteries. "The battery probably will not be able to turn the engine if it is discharged to less than 70% of the battery's capacity."

In order to prevent excessive discharge of the battery when the vehicle is inactive for an extended time, Jana recommends connecting the batteries to an appropriately rated trickle charger, or disconnecting the negative battery cable to prevent excessive discharge.

But how do you do that when the batteries are on the truck?

Purkey suggests taking the battery problems off the truck entirely, and moving them to the "battery room," an area in the shop where battery service and maintenance can be performed and batteries can be segregated into groups such as ready for service, in testing/charging, warranty, and scrap.

Maintaining an inventory of charged, ready for service batteries allows technicians to pull ailing batteries, replacing them with freshly charged batteries to get the truck out the door as quickly as possible.

"The batteries just taken out of service can be diagnosed, charged and made ready for service again without tying up trucks," Purkey says. "Once the batteries are tested, they should sit an additional two days, then be re-tested to ensure they are good enough to be put back into service."

Charging is key

Proper charging is key to performance and longevity, especially with absorbed glass mat batteries, says Brad Bisaillon, strategic accounts and transportation sales manager for Trojan Battery.

"Batteries discharge during use as well as self-discharge when idle," he says. "While in storage, batteries should be charged periodically to ensure they do not remain at a low state of charge."

Bisaillon says charge time will depend on how deeply the batteries have been discharged.

"Deeply discharged batteries will take longer to charge, while those with shallower discharges will take less time," he says. Battery charging should be limited to 16 hours, and most chargers are programmed for this as a safety feature. Be sure to set the battery charger for the appropriate program for AGM batteries.

You can see that while most of todays batteries can be considered "maintenance free," that is not totally true. Maintenance and service issues may have just been shifted away from the batteries themselves, but the problems certainly haven't gone away. If you're waiting for problem-free batteries, you could be waiting a while.

The path of least resistance

The flow of electrical current can be likened to that of water. To illustrate current and voltage, take the analogy of a garden hose and a fire hose. The fire hose can deliver a greater quantity of water (amperage) at a higher pressure (voltage) than a garden hose. That's helpful in understanding why zero-gauge cable is used on batteries and starting systems, but 12-guage cable is used on lighting systems.

In the pursuit of optimum battery performance, the question arises, are your cables choking your batteries? If your high-current charging and starting cable isn't in good condition, your batteries will need to work that much harder to deliver enough current to the load, and vice versa with respect to the alternator. Interstate's Gale Kimbrough says cable testing should be part of the electrical PM routine.

"With the changes in battery technology, we may not see the corrosion in cable and on connectors we saw 10 or 15 years ago, but that doesn't mean it's not there," he says. "The cable may look pristine, but you can't be sure unless you run a load through the cable and measure the voltage drop. Anything more than a 100 mV drop indicates a problem."

As cables age they are subject to vibration, chafing, and possibly cracking of the insulation. Any opening in the wrapping is an open door to moisture, which corrodes copper wire and restricts current flow. Bruce Purkey of Purkey's Fleet Electric advises replacement cable be at least OE quality if not better.

"Use cable with tin-plated terminal ends for better connectivity and corrosion resistance," he suggests. "Better still, use a cable with heat-shrink seals over the terminal connectors that prevent corrosion from wicking up the cable."

Finally, make regular inspections of cable routing to make sure it's not touching other surfaces that could chafe the insulation. Wrap cable near sharp surfaces, and tie down loose cable to prevent movement, which can crack the insulation or allow it to chafe.

From the October 2012 issue of Heavy Duty Trucking magazine.