Has anyone tried the knock off batteries for M18 Milwaukee tools? Reviews seem good and at less than half the price of Milwaukee, I'm considering a couple.

Use genuine Milwaukee. It's worth it in the long run.

got some cheapos for my porter cable set and they work great so far

I’m have some generic 18v for DeWalt tool. Get the highest amp rating you can find.

Save your money. Some won't plug into tool, most will draw down to 3/4 charge then quit. Better off spending more to get the real thing.

I have knockoffs for an old porter cable and a ryobi one. Both work great, hold a charge as long as id expect them to. Both had great reviews on amazon and were less than half of new ones.

I rebuild my battery packs.
Recently did 2 18v Milwaukee's for $27 each + about 20 min. of time
This was using high quality Samsung batteries

This guy has pretty good videos.

I have three Malwaukee batteries that are four years old and they work fine. Just bought some tools and got two "free" batteries with the tools. I will only use the real batteries, but i have never tried the knock offs.

I bought two 4 amp hour batteries. They worked great for the first 3-4 charges, by charge 7 they worked less than the 2 ah batteries the I replaced. Buy OEM or rebuild your own batteries.