Will this battery fit my existing Craftsman V20 tools?

Yes. It is compatible with the Craftsman V20 cordless power tool and outdoor tool lineup, so it works with drills, drivers, saws and trimmers on that platform.

How does the 4.0Ah pack compare with the smaller V20 batteries?

It holds roughly twice the charge of a 2.0Ah pack, so you get longer runtime per charge at a bit more weight. It is lighter and smaller than the 5.0Ah and larger packs.

How do I check the charge level?

LED indicators on the battery and on the charger show charge status, so you can see how much is left before you start a job.

Does the charger work with other V20 batteries?

The charger is part of the V20 system and is designed for V20 lithium-ion packs, so it can top up your other V20 batteries as well.

Is this a good buy if I already have several batteries?

It makes sense if you want a mid-capacity pack plus a spare charger for a second work area. If you already have plenty of 4.0Ah packs, the gain is smaller.