After doing the math. One Jackery 500 w battery pack at 100 % will apply 74 % charge to my Vado battery. That's 74 % usable. I found out the hard way awhile back that the last 6 % to 9 % the Motor will shut down giving no assist. The lights will work but that's it. $450.00 will get you 74 % charge in less than 3 hours using the fast charger. It's like you're taking your wall outlet with you. I was able to apply 45 % charge to my Vado from the 500 w supply unit in less that 1 1/2 hour. If you take into account the unusable 6 % or 9 % your getting 80 % or 83 % charge to the actual usable capacity of the Vado battery. During these Covid times I think it's a practical solution for range anxiety. A work around to increase your range, avoid getting stranded with no place to charge up or paying over $1000.00 for an extra battery. Also, an alternative method/strategy for increasing range than this