MarkH wrote: ↑
Sun Apr 04, 2021 2:25 pm
I have found some AGM batteries of 20aH and similar dimensions, but none have the breather tube.
How important is that?
I believe that AGM batteries are sealed with a pressure relief valve on each cell. A properly-functioning AGM battery cell shouldn't produce so much internal pressure that its pressure relief valve opens. However, when a problem that produces gas pressure occurs, the pressure relief valve should open to prevent the battery case from cracking, maybe somewhat explosively. That's when it would be best to vent flammable hydrogen gas away from inside the frunk which the standard vent tube does. However, the frunk isn't sealed, and there are fewer ignition sources in the frunk than in an Internal combustion engine compartment, so I think the fire or explosion risk would be minimal. I've read reports of i3 owners installing this type of battery with no reported problems.
Maybe you could determine the manufacturer of the dead battery in your i3. If so, maybe you could contact the manufacturer to learn whether there's a local retailer who could order this battery for you. That's what I did. However, I and the original battery's manufacturer are both in the U.S. which made things easier.
If I were in your situation, I would probably install a power sports battery while continuing my search for a battery with a vent tube. I wouldn't drive more than 180 km round-trip to pay a BMW dealer too much for the correct battery.