I don't even understand this discussion. I have a thing-a-ma-jig that plugs my cell phone/tablet/laptop into my cigarette lighter and powers them adequately. As long as I don't run down my car battery (which would be pretty stupid to do), it works fine. Charges even when my car isn't running (which could, conceivably, run down my battery).
However, the question is the tax write-off.
Sure, write it off. Just be aware that if it's over the IRS limits to be expensed, you must take depreciation and all that jazz. Maybe pay use tax at your local level (a business tax imposed on "real property", which can include shelving units, walk in coolers, etc., etc., etc. ) That means if you pay $2,800 for it, you can't just deduct the entire amount as expense, just a portion as depreciation.