For curiosity's sake, I bought a pair of "FlylinkTech" branded M12 batteries to put through the paces as well ad disassemble and inspect. After about almost 3 years of use, they passed my tests so far. The runtime is equal to the Milwaukee brand packs, and the internal construction and wiring is identical to the Milwaukee packs. The only thing I have noticed is a slightly tighter fit of the packs in some tools, needing more effort to insert and remove the batteries. I will likely try the M18 versions next, I am curious how well the rather sophisticated electronics found in those will be copied. At about half the price of the genuine article, they are definitely worth it.