About 4 years ago we purchased the cordless shear sold by Premeir One. They sell the cordless shear with extra heads. It comes with two batteries.
I also have a regular electric shear which handles the heavier shearing duties but the cordless is perfect for crunching or cleaning up the udder at lambing time or the rare surgical site clean up. They last about 6 hours of usage, hold their charge, cut through heavy wool and the cartridge sets are cheap enough to replace if you prefer not to sharpen. We bought five cartridge sets and send back for sharpening when three are dull. They cut for about 4 hours before sharpening is called for (in dirty wool) and about 6 hours in clean wool.