The Milwaukee XC 6.0 wins every event, and none of them are close. It ran the 150-watt fan for 39 minutes 15 seconds, reached 183 in-lb in the drill, averaged 6.00 seconds per lag bolt with the impact driver, and kept a weighted angle grinder turning for 6 minutes 38 seconds — about twice the next-best result. Its cells measured 5.9 milliohms of internal resistance against 12.9 to 13.4 for the knockoffs, and at 113 watt hours the pack beats its own 108 watt hour rating. It is the only one here built on 21700 cells rather than 18650s, and the only one assembled in Mexico rather than China. At $90 it costs four times a Labtec, and buy once, cry once is the pick.
If a cheap spare is genuinely what the job calls for, the Labtec is the one. It is the least expensive pack at $22 and still finished best of the three knockoffs: 25 minutes 20 seconds on the fan, 6.31 seconds per lag bolt, and 143 in-lb in the drill. More importantly, it behaved when abused — the thin interconnect inside melted at 112 amps, which is exactly what a fuse is supposed to do. Its 75 watt hours are well short of the 108 on the label, so treat a 6.0 Ah claim on any knockoff pack as marketing rather than a specification.
Two findings deserve caution. The Amityke advertises six safety features including short-circuit protection, yet it peaked at 123 amps and took nearly eight seconds to drop to zero, smoking heavily and coming close to catching fire; its cells work out to 54.7 watt hours, about half the claim, and it lasted 10 seconds on the angle grinder. The Tenmoer runs longer under load but makes no overload-protection claim and earned that reputation — after 3 minutes 33 seconds of grinding the case was smoking, the pack had fallen to just over 2 volts, and the Milwaukee charger refused it with a fault indication. All five packs survived a 10-foot drop onto a corner without damage, so case toughness is not what separates them; what separates them is what happens electrically when a tool asks for more current than the pack can safely give.