Battery Charged

If it's strong enough for the starter motor, it's more than strong enough for a few actuators. Try all the door/trunk controls, if none of them work then maybe it's an anti-theft thing, check your manual if it needs to be reset if the battery has been out of the vehicle.

My battery is in the trunk of my 2000 s 500 Mercedes. I can't get it to open by button nor key. Any one knows if the back seat pulls down?

Don't think so you need to pull cover of aux battery on pasinger front charge aux. Then open the trunk and charge the main battery