Is the DCMCS565P1 powerful enough for felling trees?

It is aimed at pruning, limbing and light cutting. For felling large trunks, a petrol saw or a higher-output cordless model is the better tool.

Does it come with a battery and charger?

This is the P1 kit version, which ships with an 18V 5Ah battery. Check the box contents for the charger, since kit bundles vary by region.

Can I use my other DeWalt 18V batteries in it?

Yes. It runs on DeWalt's 18V battery platform, so packs from other DeWalt 18V tools fit. Larger packs add runtime but also weight.

How long does the 5Ah battery last?

Runtime depends on wood size and cutting technique. Expect a useful session of pruning and light cutting per charge, with shorter runs in dense or wet wood.

What bar length does it use?

It uses a short guide bar suited to pruning and limbing rather than large-diameter logs. Confirm the exact bar and chain spec before buying replacements.