Where is the battery?

no information is published yet on the 2011 model, however, the 2010 E350 battery is located in the engine compartment at the firewall on the passenger's side.

under the back seat

Always best to check your manual. I have a 06' E350 and it has two batteries. The main battery is in the trunk and you have to remove the spare to access it. The second is a small gelpack battery to maintain electronics and stuff located at the firewall; it is like a small scooter or mower battery. They both went about the same time. Witht he Gel battery I got red warning lights on the instrument display. Can't miss that. Hope this provdes some help. I know it is not for a 2011.

I have a 2011 M-Benz E350 and my battery is under the hood near the firewall on the passenger side. The battery has a black plastic cover on it that you can remove by un-doing three metal clips.