I must have retarded lead acid batteries, or a crappy charger. I've never seen a car jar take 0 amps. It seems that it will always try to take something. The lower that something is, the less the battery generates in water loss, but given enough volts, they will get some amps forced into them, which I assume ends up as resistance in the electrolyte, and heat being generated, and micro tiny bubbles floating up to the surface.
At least, that's been my observation, someone correct me if I am wrong, or my eyes and ears are bad. I was a lot younger back in the days of being a Sears Diehard battery and power train tester/installer in the late 1970's, I may have forgotten a few things since then.