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.
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.
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 today's 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.