I am really curious. What is the normal amperage current when the car is off these days? I imagine the computer is still looking for input. What else would be drawing a current normally.
Less than 100 milliamps, usually much less.
Carmakers want that number as low as possible but the stuff they keep installing adds up, and up and up. With the number of computers in a modern car exceeding a dozen, they ALL draw a little when “asleep.” It adds up fast.
Then customers add anti-theft, remote starters and big stereos to the mix and these devices have no discipline at all when it comes to current draws when off. And they get far worse when they fail.
So consider 100 milliamps, or 0.1 amps. For a 70 amp hour rated battery (not CCW, amp-hours is important) the battery would not have enough juice to start the car below about 30% charge (more is needed if cold) so that’s an allowable loss of 49 amp-hours. It takes 20 days to render the car un-start-able with a 100 mA draw. That is a 3 week vacation with the car parked while you are gone. Not acceptable. 50 mA would be better, 25 mA better yet.
Great info, and I didn’t even need to do the calculation! No wonder we are hearing covid stories of low battery charge for those who drive very little.
Depends on the car also. My current Lincoln, past Lincoln, and the Lincoln Aviator my son used to have would draw about 700 Milliamperes when first turned off. One had to wait 45 minutes to an hour for the electronics to go to sleep before a normal draw (75 or so MAs) would appear.
On a shaky battery 700 MAs can be a problem and even more of a problem if someone has added some toys to it.
I’ve let my Lincoln sit for several months with no starting issues.