Originally Posted by 
goingbush
				
			 
			A Jerry can size of my LFP batteries is 3.2kwh = Approx 10km in my Landy or 15km in a Nissan Leaf .  
Would have been handy for me when I ran out of charge 5km from home & had to call a Flat top . I do happen to have 5 spare cells that would make up such a pack but would need to also source a suitable Inverter .
Probably make more sense dare I say to carry a small generator.
Edit,
Further to above, now you've got me thinking.
4 of the LFP 200 AHA Cells above will be 12.8v nom (13.8 max 11.6 min) Use onboard Solar Panels & MPPT to charge the 'jerry can' and a 240v 3500W inverter as a handy 240v power supply and to plug the J1772 Onboard charge lead into in an emergency , - but will only give about 10km range to your depleted traction pack, . Wait for the "Jerry Can" to charge from onboard Solar panels (might take a day or 2) & add another 10km to your battery pack . slow process but better than walking , And that 10km would become 20km when driving in "Eco mode"