Hi, I have been using this on a daily basis for the same needs as you. You do need a special cable to handle the high amps going through, otherwise your fuse will trip. A normal one will not work!
This is not quite accurate. Part of the problem is that a normal extension will work ... but it could be working in a potentially unsafe way, without the user realising it. The 10 amps that the UMC draws is within specification for a household circuit so it will not normally cause a fuse or MCB to trip. Its not the number of amps it's the fact that it will be drawing those amps for hours at a time. The amps drawn is no higher than for a normal kettle, it's just the time factor that allows heat to build up. Telsa specifically advises that extensions should be not used with the UMC ... but ... if you know what you are doing, it is safe to use an extension if it is of a suitable specification and remains uncoiled during charging.