Do these fit all DeWalt 20V MAX tools?

Yes. They use the standard DeWalt 20V MAX slide-on connection, so they fit drills, drivers, saws and other tools in that line. They do not fit DeWalt's 12V MAX or FlexVolt tools.

Is a charger included?

No. The pack is batteries only. You need a DeWalt 20V MAX charger, which you likely already have if you own DeWalt tools.

How long does one pack run?

Runtime depends on the tool and the job. Expect short runs in high-draw tools like circular saws and much longer use in drills and impact drivers.

Are these the same as the batteries that come with DeWalt kits?

They are genuine DeWalt 20V MAX packs of the same compact class sold in many kits. Check the model number on your existing pack if you need an exact match.

Can I leave them on the charger?

DeWalt chargers manage the charge cycle, but for storage it is better to keep packs cool and partly charged. Avoid leaving them in a hot truck or garage.