If it has removable caps, pop 'em off and make sure the plates are covered by at least 1/4" of acid. If they're not, add distilled water until they are. If they're good, or after you've added the water, drop an aspirin tablet down each hole and replace the caps. Not only should this rejuvenate the battery, in about half an hour it should actually start the car with no charging or jump start. No, you can't make a battery last forever this way but it should get you by until you can swing a new one. I've done this more times than I can count, most recently on the battery in my Imperial. That was almost two years ago; it sits for months so I usually leave it on a battery tender, but it does hold a charge on its own for at least a couple of weeks.Cheapest around here for a battery is 120. Mines beyond toast, I'm just waiting for stuff to sell before I buy another one.
Regular old aspirin tablets, preferably not safety-coated but no biggie if they are. No caplets, Advil, Tylenol, etc. Just good ol' regular aspirin, 375mg. It's never failed me yet.
Sincerely,
MacGyver