That's a real interesting idea about renting the aux battery. Cost and logistics would obviously be large factors. Like where are the available aux batteries stored, do they need to be shipped, does a pro need to install them, how long does the process take meaning how much time in advance do you need to reserve one, is there a min/max time to rent them, etc.will it be sold as an accessory for more permanent capacity and/or perhaps Rivian will rent these batteries out for owners who need it for one-time use?
What's also interesting about this idea of renting is the possibility of a third option. A Rivian owner decides not to initially get an aux battery as they see potential in renting them later on. After a few rentals, out comes the calculator. Owner determines the frequency of needing the aux battery, and factoring in less cargo space and increased weight of the aux battery, it now makes sense to buy one. So instead of renting an aux battery, will Rivian (or OEM?) provide a means to buy an aux battery *after* the initial purchase.