Best way to burn some juice of a couple runners?

[BiduleOhm]

Yes, the extension cord wire is thin and long enough to have a high enough resistance

 

[BarkingSpider]

Exactly, its the same reason, your power tools don't work so well at the end of a long extension lead, its due to the voltage drop caused by the resistance of the long leads. Low voltages are particularly effected, that's why the utilities use super high voltages for long distances.

Look at my photo above, bridge the +/- ends of the 50ft cable so the wire becomes 100ft long.

Only connect the battery until the wire becomes hot, then disconnect till it cools down. The actual time will depend on the thickness of the wire and the length.

 

[BarkingSpider]

I just tested the extension lead method above with a brand new 280ah LifePO4 cell.
I used a 14 gauge 50ft cord with a simple loopback (yellow wire below) making the wire 100ft long.
The total wire measured 2 ohms, 1 - 10 ohms is the sweetspot.
There were no sparks, nothing eventful connecting the wires.
No wires got hot, not even slightly warm
I checked the voltage every minute with a multimeter
The voltage dropped from 3.6v to 3.3v in 15 minutes
All in all, a success. I would recommend this method.

 

[Maast]

I use 16 gauge test leads and 14 inch lengths of .032 stainless safety wire I got at Lowes. One length is about 5A of draw at 3.2v. The wire will get melting plastic hot, but not red hot.

 

[BarkingSpider]

I use 16 gauge test leads and 14 inch lengths of .032 stainless safety wire I got at Lowes. One length is about 5A of draw at 3.2v. The wire will get melting plastic hot, but not red hot.

I use this exact method to make a hot wire for cutting polystyrene blocks with no mess.