I'm not looking to charge the primary battery. I am looking for a way to add an additional battery pack that the electric motor can draw from.

not a 25 watt backpack, but a reall cell. a 250+ watt solar cell would fit on the roof of the truck . probably more than 250 because a 250 fit on a prius roof!

If that cell was to charge a secondary battery pack and have that piggy-back into the primary battery that could be a meaningfull charge. That would be 1 to 2 KW of free energy.

(250+ watts x 8 hours of sunlight while parked at work could produce 1 to 2 KW of energy not saying 2 KWHs because I am factoring in pitch of both the sun and the 0 degree truck roof, but also consider most of the US sees more than 8 hrs of sunlight a day).

Since 1 BTU is the same as 0.293 W-hrs, or 0.000293 kW-hrs
1 gallon of gasoline has 125000 btu's.
125,000 BTU x 0.000293 kW-hrs/BTU = 36.625 kW-hrs.
Therefore, one gallon of gasoline contains 36.625 kW-hrs of energy.

this is the same as getting 1 free tank of gas a year

Or, 12000 mile/year truck that averaged 28mpg, would see it's mpg increase to 29 mpg.

No offense, but I want to know if there is anyway to add an additional battery bank. I wanted to know if by running the secondary through the 12v if the primary would draw off if it. I wanted know if my idea would work, and I am not looking for someone to discourage me from trying based on what they believe to be insignificant.

But thank you.