Does the Einhell TE-CN 18 come with a battery?

No. It is sold as a bare tool, so you need a separate 18 V Power X-Change battery and charger. If you already own Einhell 18 V tools, you can share their packs.

What length nails and staples does it take?

It accepts 15–32 mm brad nails and 16–22 mm staples with a 5.7 mm crown. That covers trim, upholstery and thin panels, not framing.

Is it strong enough for hardwood trim?

It is a light-duty tool. Owners report good results in softwood, MDF and fabric but say it can struggle in dense hardwood.

How fast does it fire?

Up to 20 shots per minute, which is fine for trim and upholstery but slower than corded staplers.

How many fasteners does the magazine hold?

100 nails or 100 staples, so reloads are infrequent on small jobs.

Is it worth it over a corded stapler?

If you already have Einhell 18 V batteries and want cable-free use in awkward spots, yes. For heavy or continuous work, a corded or pneumatic stapler is stronger.