Today’s vehicles are loaded with electronics that add high demands on the battery and charging system. Most cars will draw a small current from the battery to run things like the clock and other vital computer modules even when the key is off.
Computer modules are programmed to go into a sleep mode to cut power consumption after the ignition has been switched off. But the power drain can be up to 100 milliwatts for 30 minutes or more after the engine has been switched off.
Vehicles with a smart key fob can activate the keyless-entry system and other modules, increasing the power drain on the battery. Consequently, if a car isn’t driven for a week or more, the battery can drain to the point where it may not crank the engine.
Loose, corroded or damaged battery cables make poor electrical contact and can cause a battery to run down or a no-start condition. Be sure to inspect battery cables and clean or replace as necessary if you encounter starting/charging problems or install a new battery.
Batteries in hot climates typically need to be replaced sooner than in more moderate climates by up to two years. The heat causes the electrolyte inside the battery to evaporate, and once the level drops below the top of the lead plates, the plates can be permanently damaged. Adding insult to injury, there is no way to add water to “maintenance-free” sealed batteries.
Consequently, batteries with this condition will become damaged if their water level gets too low. Lead-acid batteries have been a mainstay in vehicles for decades, but with new power demands, many OEMs are switching to longer-lasting absorbed glassmat (AGM) batteries. The sealed, glassmat design is more reliable, but they’re more expensive than the traditional “flooded” battery.
AGM batteries drain at a much lower rate than flooded types. Higher amp hour AGM batteries also can discharge more deeply and recover repeatedly under vehicle alternator charge or through maintenance charging. A standard flooded-cell battery can’t handle this type of cycling without failing prematurely.
With all of the electronics in modern vehicles today, changing a battery isn’t as simple as it once was. If you change a battery without hooking the cables to an auxiliary battery, you may lose radio presets or important PCM information. The vehicle must relearn and cycle through the OBDII emissions tests to bring everything back to normal operating conditions, and that’s just the electronics in the engine.
There are many modules connected through the controller area network (CAN bus) that can be affected when a battery isn’t replaced correctly. Jump starting a vehicle with jumper cables from another car, for example, can cause voltage spikes that may weaken or destroy the battery cells in both vehicles. If you must jump start a customer’s vehicle, use an auxiliary starter battery, or a battery pack that won’t spike the voltage.