alohart wrote:If that happens to your i3, it has a serious abnormal 12V load that needs to be fixed, or the 12V battery is bad. For a healthy 20Ah battery to be fully discharged in 5 minutes, the load would need to be 240A! But if the 12V battery is unable to hold a charge, is partially short-circuited, etc., it could discharge quickly under the conditions that you describe. But that's not normal behavior for an i3.
That was just an example. The fact is that many i3 owners have used the emergency charging port opener, and that means that the 12v battery was flat. In my opinion this will not happen with the 40ah battery. This fact alone for me is enough to justify 7lbs more for a 40ah battery.
alohart wrote:Our Honda Insight has a 16Ah AGM battery that is 7 years old and still going strong. That battery has even less capacity than the i3's 20Ah battery. Like the i3, out Insight does not use a 12V starter motor, so the 12V battery powers only its computer modules and accessories and is able to do so without being seriously discharged due to a lack of capacity. So all evidence suggests that a healthy 20Ah battery is sufficient for an i3.
Not sure what both cars have in common. With i3, if your 12v battery is dead, your car is dead. You may have 100% charge on the HV battery, but no way to operate or drive the car.
My 1988 BMW 325i will start right away after sitting for a months and the battery is only 45Ah. Most modern BMWs, and most modern cars for that matter, would be dead in the water after a month sitting, and they have much bigger batteries.