Backup Battery for low battery scenario?

[Iamthecaliflower]

High Capacity Backup Battery Will Keep You Powered For a Week

Let's assume you need to drive around 300miles straight, for some reason. However, for some reason you only get 270-290miles per charge. Would it be possible for something like the above device to give you enough juice for say an extra 100-300miles, assuming there isn't a charging station near by where you run out of juice? In theory, this might only cost an extra $500-1000, if that. Would this further help with range anxiety? Does something like this exist?

[VolkerP]

From the linked data sheet:

$62
Ultra reliable lithium ion battery with 9900 maH capacity at 5v output voltage
Weight (main unit): 8.6 oz = 244g

That makes for 49.5Wh of energy. Model S uses 300Wh per mile so not much help here. If you calculate kWh/kg or kWh/$ it loses out against Tesla battery pack by far.

There is no reasonable way that an extra battery helps with range after your main battery passes out. Always better to have all batteries contribute their power all the time & absorb energy from regenerative braking. This transcribes in better warranty terms for the larger Tesla battery packs.