McM;
Having to buy a Faraday pouch - nor exactly an advantage.
Don't like anything in my pockets, esp when driving. Inevitably get chucked on pax seat and end up goodness knows where.
Battery - car battery (based on what others were saying above - no personal evidence hence my '?')
Currently have stop/start & keyless so yes, I do have to think about whether I've switched the engine off. I'm usually distracted by trying to find my darn keys. (I'm often in command of a larger, much heavier a/craft that happens to be keyless as well so I think I'm ok to be let out now and again - only just).
Money? yes, that was my point.
So what IS the advantage of keyless?