Q: I have a 2001 Lexus ES 300 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 harm to the vehicle?

A: 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 and haven’t broken one yet.

Q: 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?

A: 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 part may 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 is more likely to bring the engine up to operating temperature, which should reduce wear and emissions, improve fuel economy and helps boil off sludge in the crankcase. You might ask him if he plans to renew belts and hoses, coolant, and brake fluid every four years. Even though they may not be prescribed in the maintenance schedule, doing so is a great insurance against some potentially costly outcomes.

— Bergholdt teaches automotive technology. Email questions to under-the-hood@earthlink.net.