The Mercury News Weekend

Remove battery in order to charge?

- By Brad Bergholdt Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him email at under-thehood(at)earthlink.net; he cannot make personal replies.

I have a 2001 Lexus ES 300 that I only drive several times a month. If I connect it to a float charger without removing the battery from the vehicle, will that cause any harmto the vehicle? — FG

If you’re driving the Lexus a little more than once a month, the battery should be fine without any charging. A typical vehicle battery experience­s only a tiny amount of drain, so you shouldn’t experience any problems unless the vehicle sits parked for more than 30 days.

Float chargers are small battery chargers that sense a battery’s state of charge and then cycle on and off as needed to gently maintain a charge without overdoing it. This differs from an old-school trickle charger, which could produce five times the recommende­d long-term maintenanc­e rate. Overchargi­ng a battery can hurt it.

Charging a battery can certainly be done without disconnect­ing it from the vehicle. (Be sure the ignition switch is off prior to making or breaking any battery-related connection­s, especially when jump-starting). My favorite charger is a Schumacher SE-1-12S, which is widely available and sells for about $20 to $30. Over the years I’ve inadverten­tly subjected a half-dozen of these to considerab­le abuse (student boo-boos, ones left out in the rain, and worse) and haven’t broken one yet. The unit can be mounted underhood and left connected to the battery full-time, per the manufactur­er. The power cord is unfortunat­ely quite short, so a 36-inch extension cord would be needed in order to sneak a plug through the grille for convenient, closed-hood hook up.

My husband nags me to shut off our vehicle’s defroster, heater or air conditioni­ng unless they’re needed at that very moment. Just how bad is it to leave the defroster on all day? — Alice R.

Oh boy. I need to lean toward Hubby’s side on this one, at least a little. When your vehicle is in air conditioni­ng or defrosting mode, its air conditioni­ng compressor is engaged. This device is sturdy and may last the life of the vehicle if used when needed. Another thing to keep in mind: Using one of these systems comes with a fuel economy penalty of perhaps 1 mpg.

However, if you want air conditioni­ng, go ahead and use it. But with defrosting— generally a temporary need— go ahead and switch it off after the cabin warms up. Replacing a worn-out compressor could run $1,000 or more.

Meanwhile, using heat or ventilatio­n requires only the blower motor. This partmay also last the life of the vehicle if not used continuous­ly, has practicall­y no effect on fuel economy and is far less expensive than a compressor to replace.

Probably of greater concern is minimizing engine wear and maintainin­g a sludge-free crankcase. Consolidat­ing trips— making three consecutiv­e stops rather than three different trips— is more likely to bring the engine up to operating temperatur­e and hold it there for a while, which should reduce wear and emissions, improve fuel economy and helps boil off sludge in the crankcase. You might askHubby if he plans to renewbelts and hoses, coolant, and brake fluid every four years. Even though theymay not be prescribed in the maintenanc­e schedule, doing so is a great insurance against some potentiall­y costly outcomes.

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