You may be seeing another “positive” service-related trend in your shop — increased battery sales.

Some market analysts are predicting that battery sales in cars and light trucks will grow, as more vehicle batteries are dying young.

As you already know, car batteries normally need to be replaced about every three to five years, depending on customer driving habits and climate conditions.

However, some shops are seeing this replacement interval shrink to about two years, which is probably making some of your customers question the quality of the replacement battery you install.

But you know it’s not the battery quality that’s in question. The real culprit you need to educate your customers about is the plethora of gadgets, such as cup warmers, personal electronics chargers and other onboard systems, that sap power from a battery like Kryptonite draining Superman’s powers.

According to a recent Wall Street Journal feature, one New York shop that specializes in modifying sports cars to improve their power, speed and handling has lately taken on the task of tending to its customers’ batteries due to add-on electronics like iPods and navigation systems.

And even in your own shop, you probably noticed over the past decade how your customers’ cars, SUVs and minivans have evolved from basic transportation to offices or living rooms on wheels. While servicing these vehicles, you may have observed the growing range of battery drainers — from DVD players with wide screens to the booming subwoofer sound systems or mood lighting — all installed around the very vehicle you are trying to repair.

Heck, you may even have a refrigerator or cup holder that heats cocoa and coffee or cools your favorite soft drink in your own vehicle that’s used to get you to your favorite fishing hole or off to the next auto race.

But it’s not just the driver’s cell phone chargers, laptops and other handheld gadgets that are putting a strain on the battery. There’s quite a bit of electronics in the design of today’s vehicles that pull power even when the vehicle is shut off. For example, electric fans to help cool the engine often run for a few minutes, and navigation and engine-management systems that suck power to maintain their “brain’s” memory also lead to a battery’s slow death.

The good news for you is that all of these gadgets that make the driver more comfortable and that provide them with the convenience of home or their work is going to provide more service opportunities for your shop.

According to the WSJ article, sales of replacement batteries — which range from $50 to $200 — jumped 13% to 67.7 million in 2006, compared with 59.9 million 2005.

In the previous 10 years, according to data from Industry MR, a research firm in Oak Brook, IL, the average number of replacement batteries sold each year was about 54 million. So what do you tell a customer who complains to you that “they just replaced the battery not too long ago”?

You could recommend to them to disconnect the battery if their vehicle is parked for weeks at a time. You also might suggest they purchase a trickle charger — which cost between $30 to $60 — and can help extend battery life by keeping it fully charged when the car is parked.

Or you could just advise them that they live without their electronic gadgets and the accompanying charging units. But really, who wants to return to the “Dark Ages”?