Maybe a brand new battery on a brand new laptop. I wouldn't trust the battery in my current laptop. The laptop is about 10 years old and the battery is more than 3. It still works, but it isn't worth the trouble of running off battery power, having it fail, and then frying a PCM.

As to the hardwire reason, I don't trust cigarette lighters for powering a laptop via inverter while programming a PCM. Especially the inverter I have, which is about 400W. The max you are going to get out of a cigarette lighter is 150W, which can cause you problems.

I have mine wired with 8 gauge wire. Sure, it's overkill, but it doesn't cost much and takes maybe 15-20 minutes to run. Better safe than sorry, in my opinion.