How bright is 3000 lumens for a camping lantern?

It is roughly two to three times the output of common 1000 to 1500 lumen lanterns. That is enough to light a whole campsite or a large room, not just a picnic table.

How long does it run on batteries?

Runtime depends on the battery type and brightness setting. Expect the longest life on low modes and the shortest on the full 3000-lumen setting, so bring spare batteries for multi-night trips.

Is it good for backpacking?

Not really. The aluminum body and 9-inch height make it a car-camping or emergency light. Backpackers are better served by a small, light lantern.

Can it be used indoors during a power outage?

Yes, but run it dimmed or bounced off a ceiling. At full output it is bright enough to glare and will drain batteries fast.

What batteries does it take?

The listing does not specify a battery type. Check the label or manual before buying, and confirm whether it uses standard cells or a rechargeable pack.