Expanded battery option on BEV

Remove heat pump and go with REx resistance heat for cabin.

Put in air cooled supplemental batteries (like Leaf and as opposed to water cooled 24 kWh standard batteries) in space where Rex (or heat pump) sits.
Air cooling will reduce both weight and cost and is "workable" for supplemental batteries.

Put heat sensor inside supplemental battery pack so that if batteries start to overheat in charging, they are shut off until they cool down
(Existing 24 kWh battery continues charging with water cooling).

Discharge batteries using full set in parallel, but turn off the optional air cooled batteries if they get too hot during discharge, until they cool down enough.

My guess is the supplemental batteries would be 10 to 12 kWh extra. A heavily discharged i3 with supplemental batteries would take longer to charge and might not discharge fully in some cases.

Any thoughts ?

Your suggestion is the put in an air-cooled supplemental battery of 10 to 12 kWh, and remove the highly efficient heat pump.

This would require two battery temperature management systems, and result in a variable battery capacity and life of the two batteries. Losing the heatpump would impact efficiency, as would the extra weight of the additional battery. Putting that much battery at the back of the vehicle would also effect the weight balance. One of the reasons I didn't buy a Leaf is because of it's poor battery thermal management.

The current expected battery capacity increase is by replacing the existing cells in the current battery pack with higher output cells. This method would require minimal change to the cars weight and management systems and allow the heat pump to remain. Basically we would get the exact same vehicle with a substantial capacity increase and still have the capability for a heat pump or REX.

There's a direct correlation between vehicle weight and maximum range...adding more weight to a chassis by adding more batteries (as opposed to making the existing ones more powerful) decreases the overall efficiency. Take a look at the Tesla...nearly 4x the battery capacity, but it does not have 4x the range. Adding more weight is evident in just the i3 between the BEV and the REx versions, where the added weight of the REx slows it down, and gets a lower EPA mpge rating. If you want longer range with the i3, wait for the 2017 MY. If you want even more range, wait for some of the newer platforms, but they will almost certainly not be as efficient. If you really need more range from the i3, you probably bought the wrong car! It is what it is and works quite well at what it does.

It's a silly Idea, I'm siding with Jad ^^. If you want more range buy something with more range from the outset , trade up, or wait until details of any battery upgrade options become available from Mid '16. Even then it is likely to be an uneconomic pathway, much like what you propose.