My Lance had a compartment for one battery. The first battery was an Optima, I went through three of those over a three year period. They just went bad. I put in a group 31 AGM in year four, I think. Then I added a second battery under the wing of the TC. I used 8ft of marine gauge no 4 cable with an Anderson connection. I ran this set up for about six year without a problem. Last year the older battery went bad so I bought two new ones.
The point being the battery's were not the same age nor manufacture and I got good service from my set up.