Ralph - I noticed in the video, two car batteries on the garage floor. Unfortunately, while they are on cardboard, the cardboard isn't sufficient to insulate the batteries from the colder concrete which is colder than surrounding air, typically 5-7°F.
Voltage between plates depends upon their temperature and the temperature difference from top-to bottom of battery plates induces self-discharge. You need at least 3" of wood or equivalent to keep the battery plate temperature differential to be near zero and prevent charge from leaking off. In addition the temperature induced acid flow will cause the lower portion of the plates to deteriorate, lessening both their capacity (CCA) and their life.
If anyone is still reading and has a weather/insulation expertise ... QUESTION is there a decent inexpensive way to treat one's garage door soas to get the garage perhaps to 50 degrees. I can't conceive how to manage the cracks around the door before going to the next step of adding a safe heater to the 12x20' work area. With my Merc on jackstands, I've a host of things to do but my aged body unable to cope with the temperature including laying on the concrete.
Using my newly acquired (we just got a Harbour Freight store in town - one of those new ones every 3 days) $15 HF IR gun. The ground outside is 19°F, (no wind) inside garage doors measure 32°F, concrete floor is 35°F and everything else in the garage is 37°F. House is 69°F with baseboard heaters on full time. Ahh Costa Rica. Back to the IR gun, it calibrates pretty close going from ice cubes to boiling water. Worth $15 anyway.