It's so small I first thought it was an auxiliary charger for a cell phone. Maybe with an outlet on the dash.
But with the 'battery accepting charge' notice, maybe it is a charger for your Chassis battery...at least all those I'm familiar with charge the chassis batt because often, the manufacturer doesn't add an auxiliary charger for it. It's mostly charged by the alternator.
Mine covers nearly the entire top of the AC, and it's only 8 Watt. Useless.