I haven’t charged my Apple Watch for several years. It won’t charge does it need a replacement battery

Yes, it probably needs a new battery. A lithium-ion battery that has been allowed to sit in an uncharged state for an extended time may become unchargeable. Of course, the other question is whether or not it's worth replacing a battery on a watch that old.

In addition to what IdrisSeabright offered, Apple doesn't actually replace batteries in Apple Watch. Instead, they offer, for a fee, a refurbished, like new Apple Watch. This only applies if the watch is not obsolete. If it is obsolete, your only option would be to recycle the watch and buy a new watch if you want an Apple Watch. I agree that if the watch is pretty old, it would likely be a better investment to just buy a new watch.