In a conversation the other day, T.H. told me that her relatively new battery sometimes fails to start her car. That likely happens because her trips are too short to fully charge a semi-drained battery. Today’s vehicles draw some battery power for computers even when not being driven. Besides that, during winter drives, alternator amperage for recharging is reduced by operation of high-draw items like heated seats, defrosters, heated steering wheel and heater blower motor.
Otherwise good batteries can easily drop to 50 percent or less of a full charge while sitting. They may even still start your car, but will have no chance of reaching full charge quickly while driving with lights and accessories turned on.
For vehicles driven minimally, and for those that are not driven at all for over two weeks, a small battery charger is your best ally. Many small chargers designed for this purpose charge at only two amps, and automatically drop to a milliamp “maintenance” charge rate when the battery is fully charged. Using one will help assure that your car or truck will start when you want it to.
One small charger I use indicates when a battery is below 90 percent charge, when it reaches 90 percent, and when it is fully charged. I attach it to all of my vehicles about every 10 days whether they have been driven or not, and they are always below 90 percent when the charger is first attached. Still, I usually replace my “7-year” batteries at 5-6 years to assure dependability.
A reader once asked if it is necessary to remove battery cables to charge a battery in the car. No, it is not — I know of no requirement to disconnect vehicle battery cables before charging a battery in a vehicle. Chargers should not be emitting any detrimental voltage or amperage different from what your battery itself or your alternator “gives off.” Virtually all modern vehicles use 12 volt, negative ground electrical systems — use a matching charger. Also make sure the ignition key is in the off position and lights are off when charging.
Most instructions say to place the positive lead from a charger or jumper cable to the positive battery post, and then connect the negative lead to a remote ground (frame or engine block). This is to avoid a spark that could ignite the gasses coming from battery vents. I connect chargers directly to the posts, but I make sure that the charger is unplugged or switched off until the connection to the battery is completed — this will insure that no unwanted sparking occurs while connecting leads. For jumps, I connect cables to the dead battery posts directly, then the positive lead to the jumper battery post, then the negative lead to a remote ground on the jumper car. Newer cars have a remote positive lug as well, so both cables can be kept away from the battery during a jump.
I mainly use 2 amp “trickle” or “maintenance” chargers, as I am dealing with batteries in the upper range of charge state. For totally discharged batteries, I use a 20 amp automatic charger that starts at a higher “quick-charge” rate, and then decreases the rate as the battery becomes charged. Slower charging assures that all of the cells will be evenly and totally charged.
Though winter is waning, year-round battery tending is recommended for semi-idle vehicles.
Readers may contact Bill Love via e-mail at firstname.lastname@example.org.