It pays to read your warranty carefully.
Most warranties require the purchaser to return the unit for repair, this is normal practice and one of the reasons you are better to buy locally if possible and the gamble you take when you buy from futher afield or overseas.
For example, my 3 month old ride on lawn mower broke part of the steering arm. I had to pay a towing service to take it to the mower shop I purchased it from, the shop fixed it for free under warranty and I paid to have it returned.
Some warranties only cover replacement of parts, but you have to pay for the labour to replace the part. Example is Gazelle Nexus rear wheel spokes breaking within the 2 year warranty, Gazelle supplied 36 new spokes but the owner had to pay for the wheel to be rebuilt with the new spokes! (there is currently a 12 week waiting period for rear wheel spokes from Gazelle).
I wish you good luck with getting some better service from the seller as the battery tester looks like a nice unit for e-bike repair.