where is auxillary battery located in a 2010 e350

Hello, per the shop manual, I'm seeing one is located in the spare tire area of the trunk, and one is located under the driver's dash area.

The aux battery on your car is behind the under-dash panel on the driver's side by where your left foot would be if you were sitting in the driver's seat. It's small, about the size of a brick and similar in weight. --Quality Motors European Team