Battery Charger?

I park underground where I have no AC outlet for electric power. I don’t drive my gas powered vehicle much so the battery goes weak, then dead.

I'm not looking for a jump starter. I’m looking for a battery charger that works like this.., I charge a portable battery device using my home's 120ac outlet. I take the charged device to my car and use it to top off my weak car battery. I’ve looked everywhere but can’t find such a charger. Do they exist?