Press the button on a Ryobi ONE+ pack, and four green lights feel like a full tank. I've trusted that little display on every pack in my shop, from the compacts that came bundled with tools to the 6.0Ah battery I grab most often. The gauge, it turns out, answers a narrower question than the one I was asking. It reports a charge band rather than how long your tool will run, and those bands aren't evenly sized.