1500W over 12 hours?
that is a LOT of power. a gaming computer runs at most 500w
heat up rocks on your BBQ outside and swap them in every hour to keep the lizard warm. that would be the cheapest best plan.
otherwise buy a marine battery and a 12 volt electric blanket and see how long it lasts https://www.amazon.ca/Electric-Blanket-Supplies-Constant-Temperature/dp/B0B7KW3DPG/ref=sr_1_6?crid=3C4Q5TXVOM9I1&keywords=12%2Bvolt%2Bblanket&qid=1671838046&sprefix=12%2Bvolt%2Bplanke%2Caps%2C307&sr=8-6&th=1