Q: I have a 2005 Hyundai Tucson with 90,000 miles on it. I've never had a problem since I purchased the vehicle, but I'm worried the battery will fail sometime soon because of its age. I'm planning to change the battery myself but I'm concerned about the computer and electronics due to the temporary loss of power during the replacement process. What should I do before and after changing the battery?

A: Just drive the car. Replacing the battery, which of course requires disconnecting the vehicle's electrical system from the original battery, will do no harm to the vehicle's electronics. You'll likely have to reset the radio station pre-sets and the engine management system will take a few miles of driving to "re-learn" your driving characteristics, but you probably will not notice anything.

Perhaps the more relevant question at this point is: Should you replace the battery now or wait until it fails? Being a founding member of the "Snug America" club and not wanting to part with any more of my hard-earned dollars than absolutely necessary, I lean toward the latter. Most batteries will develop symptoms of impending failure such as slow engine cranking speeds, giving you a heads-up that it's time for a new one. But batteries can and do fail suddenly and completely without warning.

So when I suspect a battery might be on its last legs, I carry a portable battery booster in the vehicle. Then, if the battery does fail, — at any time and for any reason — I can jump-start the vehicle to complete my trip.

This, by definition, is the Murphy's Law of automobiles — if you have a spare part with you, you'll probably never need to use it!

And finally, to put your mind at ease, have the original battery tested at a local parts store. A load test or electronic test will give you an idea of how much life your battery still has.

Q: I have a '93 Buick Riviera with the 3800 V6 engine and 182,000 miles. When I start the engine it makes a "thudding" noise four to five times. It has done this intermittently for the past three years. One mechanic told me it could be a cracked flywheel. Can you help?

A: Does this noise primarily occur on a cold start after the car's been sitting for at least several hours? Also, watch the oil pressure warning light carefully as you start the engine — do the "thuds" last precisely until the warning light goes out? If so, the noise may be due to worn main or rod bearings. Once oil pressure is up, the excess clearance is buffered by the oil film and the noise stops.

A cracked flex plate/flywheel or loose torque converter mounting bolts could cause a similar noise, but for three years without some type of failure? Other possibilities include a broken or failed engine/drivetrain mount or an engine startup misfire.

Regardless of the cause, at 20 years old and nearing 200,000 miles, I'm not sure I'd be willing to spend much on repairs. If the vehicle is still nice, keep an eye out for a used or rebuilt engine. Remember the automotive version of Murphy's Law.

Q: We have a 2008 Buick Lucerne. This fall we will be leaving the state for about seven months. Should we disconnect the battery? Will this mess up the computers? Also, should I use a trickle charger or a float charger? What's the difference?

A: I recommend disconnecting the battery — it is safer and will cause no harm as described above — and connect a float charger or battery maintainer like Battery Tender to keep the battery safely charged while you're away.

A trickle charger continuously charges the battery at a low amperage rate, which can lead to overcharging and battery failure. A battery maintainer charges and holds the battery at its optimum voltage safely for an indefinite period.