40V Lithium-ION 4.0 AH Battery

What you are looking at is 40V Lithium-ION 4.0 AH Battery by Ryobi, a product. Between versions of the same thing, it is usually the details — capacity, finish, what is included — that separate them. Read the setup notes before first use; most early problems come from a step skipped at the start. Where one is discounted, compare the size and edition rather than the headline alone. Keep the packaging and paperwork until you are sure it is a keeper — returns are simpler with both. Add delivery to the cheapest price and you will see whether it is genuinely the best deal.