The battery spec Ryobi and Milwaukee don't put on the box (and why it's a big deal)

We all love our cordless power tools, especially with how easy it is to snap on a battery and get to work. And even though many of us own several tools from big names like Ryobi or Milwaukee, knowing which battery pack is the best one to buy or use is still somewhat confusing. That's by design, and here's the battery spec that neither brand puts on the box or label.