Q: I like to purchase cars new and hold them for 15 years. For my next purchase, I am contemplating a gas-electric hybrid vehicle. What is the probability that the battery pack will last 15 years? If it has to be replaced before 15 years, what is today's average replacement cost?

K.A., Syracuse, New York

A: The U.S. Department of Energy says that the advanced batteries in electric vehicles are designed for extended life but, of course, will wear out eventually. Several manufacturers of electric vehicles are offering 8-year/100,000-mile battery warranties. The National Renewable Energy Laboratory says that today’s batteries may last 12 to 15 years in moderate climates, 8 to 12 years in extreme climates. Replacement costs range from $8,000 to $30,000.

Q: Thanks for your wonderful and often funny insight. I have always been told that on gas-powered vehicles, the faster you drive, the more gas you burn. Hence, the drive 55 mph. Does that also apply to electric-powered vehicles? Is there an optimum speed?

P.G., Niles, Illinois

A: The impact of vehicle speed, or more specifically drag, applies to both gas vehicles and EVs. The faster you go, the more drag you create. The optimum speed for all cars is probably 55 mph. Additionally, much depends on terrain, passenger load, driver behavior and outdoor temperature. These factors impact vehicle fuel economy in miles per gallon or per kilowatt. Ask to see my “I Can’t Drive 55” T-shirt. Care to see the formula for aerodynamic drag?

Q: My 2023 Volvo V60 Cross Country wagon requires premium fuel, minimum 91 octane. Around Chicago, premium grade fuel contains 10% ethanol. In Wisconsin, premium fuel does not contain ethanol. It is referred to as "recreational gas" at one of the big brands. Both are at least 91 octane. Is there any harm in using and/or mixing ethanol added gas with 100% gasoline?

B.T., Wheaton, Illinois

A: Any combination is safe for your engine. As a matter of fact, gasoline without ethanol provides slightly better fuel economy to the tune of roughly 2-3%.

Q: My buddy has a 2013 Mercedes C300 with low mileage. The camshaft sensor light came on, so he took it to a Mercedes dealer. They told him that there was an oil leak and it was leaking on a computer wire harness. The cost of repairs would be $8,000. He took it to my mechanic who replaced the sensor for $160 and the light has stayed off for two months. What do you think?

R.S., Chicago

A: I think it never hurts to get a second opinion.

Q: After reading your article about AGM batteries, I was reminded that the average car or truck battery lasts about 3 to maybe 4 years. I live in the Chicago area for six months, and in Las Vegas for the rest of the year. I use a battery tender on each car so that we can fly back and forth. One vehicle has a 6-year-old battery and the other vehicle has an 8-year-old battery. I have got to believe that these battery monitors help batteries live longer.

T.H., Orland Park, Illinois

A: Keeping batteries charged, or at least 80% charged, keeps the chemistry in balance. Deep cycling or allowing batteries to go dead shortens their life. So, yes, using a battery maintainer keeps the battery voltage up to snuff.

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