Depending on the tire and its appropriate inflation pressure and depending on the "12-volt power inflator," you may find that you will not get enough pressure by this method to adequately inflate the tire. Car tires typically need less than 40 pounds and bike tires almost always want more than that.

A decent floor pump can be had for $50 or so and will last a long time, probably more than 10 years, although you might have to replace or at least lubricate the rubber ring at the end of the piston. Also, you are going to need a pump to carry with you if your bike is to act as a substitute for a car. Not a floor pump, but apparently something you don't have now.

You don't say what your "run of bad luck" has been specifically but a decent LBS will recommend a pump and probably even allow you to exchange it for a different model if you can articulate a reason that was not obvious when you tried it out in the shop at the time of the initial purchase. Something as simple as Planet Bike should do the job. There are few things that are easier to buy in a bike shop than a decent pump. I do realize not everyone has a decent bike shop close-by.