Battery Device and Switch under drivers seat

[Hetken1]

I need to understand what is the device under my drivers seat on my 2005 Lexington 210. This is a recent purchase and I am still learning.
My questions are:
-What is the device and switch for that is under the drivers seat
-Now that I am installing a 400ah lithium solar system with a Li-BIM what and how do I consider the existing system,,All is clear for my solar install except the connecting/dis-connecting to the existing system.
Ken

[TZ VI Mi.]

Ken, Are you referring to the "Battery Boost" switch? It is there to temporarily bridge the "house" battery to the coach in the event of a low battery situation causing a no, or slow crank when trying to start.