Assemble Peltier Cooler to Li-poly Rc Battery
You need an MPT converter + LiPo BMS + a thermal delta T power source to harvest the energy in a firm but not over stressed mechanical design.

The temp drop must be maximized while staying within limits to maximize current source with its intrinsic internal ohmic resistance.

In other words, you challenge is get a hot-side heat exchanger, a cold-side heat exchanger, your TEG, a compression assembly system design then an MVPT charger that does impedance matching and tracking for desired output electrical power transfer charger in CC, CV and cutoff modes.

Or in other words buy what you need to match your yet to be defined power, thermal energy transfer design, voltage, current specs, impedance for all input AND outputs in each “state” or mode of operation.

MVPT

e.g. https://thermoelectric-generator.com/product/10w-teg-mvpt-battery-charge-controller/. 

Overall it can save fuel, but still a great challenge for Design Engineers. But what you need to learn is beyond the scope of this answer.