I don't think this is the case. Lithium batteries are generally much better with deep discharge than lead acid. Trying to power a heavy load below a certain

I don't think this is the case. Lithium batteries are generally much better with deep discharge than lead acid. Trying to power a heavy load below a certain threshold voltage will quickly and permanently damage them, but generally there is a low discharge disconnect that kicks in before this point. I don't presume he'll notice any particular ill effect.