Ryobi 40v batteries really 40v？

If you're familiar with Ryobi's ONE+ line of 18v tools, you might know that the 18v Li-Ion batteries contain five 18650 cells in series. Each 18650 cell has a nominal voltage rating of 3.6v, so five in series yields 5x3.6v= 18v. The claimed 40v can't be divided equally with 3.6v cells, so something is awry. It seems far more likely that Ryobi simply doubled the number of cells from their 18v batteries, or ten cells in series. That would mean the 40v batteries are really 10x3.6v = 36v. I've disassembled several 40v batteries and I can confirm that they contain ten cells in series (or parallel strings of ten cells) so yes, they're really 36v batteries.

Still not convinced? Try visiting Ryobi's websites for buyers outside of North America such as Australia or UK You'll find that the tools and batteries which are marketed as "40v" in the USA and Canada are more correctly marketed as 36v elsewhere.

Why would Ryobi call these 40v batteries instead of 36v batteries?

I'm suspect this was a marketing decision, and that Ryobi execs believed that "40v" would sell better than "36v". To be clear, calling these batteries and tools "40v" is not technically wrong. The cells inside have an operating voltage range of about 2.7v-4.2v, and ten are placed in series, so the operating voltage range of the battery is 27v-42v. IMHO calling these batteries 36v would be the "most correct" choice, but technically any value in the range of 27v-42 could be considered correct.

Many manufacturers do or have done this sort of thing.

Remember the Ryobi TEK4 line of tools, which utilizes a rechargeable "4v" battery? The battery is really a single 18650 cell with a nominal voltage of 3.6v. But calling the line TEK3.6 doesn't sound as catchy as TEK4.

How about the Craftsman C20 line of 20v tools? The Li-Ion cells in these batteries were five 18650 cells, so the nominal pack is 18v.

How about the DeWalt 20v/60v Flex line? These are really 18v/54v.

I could go on, pretty much all manufacturers do this.

Part of the reason for this may have to do with cell chemistries. At one time the most popular cell chemistries were Nickel Cadmium (NiCD) or Nickel Metal Hydride (NiMH). The nominal cell voltage for these chemistries is 1.2v, so battery pack voltages had to be a multiple of 1.2v Popular tool lines used batteries rated 9.6v, 12v, 14.4v, 18v, 19.2v, etc. When manufacturers started using Li-Ion cells (nominal cell voltage 3.6v) the voltages didn't always align well. The 18v lines were fine, as 15 1.2v NiCD Sub-C cells have the same nominal voltage as five 3.6v 18650 Li-Ion cells. But the 19.2v batteries which used 16 1.2v NiCD cells couldn't be achieved directly with Li-Ion cells, so manufacturers used five 3.6v 18650 cells (18v) and called the batteries 19.2v anyways.

The newer Lithium Polymer (LiPO) cells have a nominal voltage of 3.2v, so if/when these get integrated into existing tool lines manufacturers will have to decide how to do their rounding. For a 40v battery that's 40v/3.2v = 12.5 cells, or for 36v that's 11.25 cells. I bet they'll choose 12 cells so the actual nominal voltage will be 38.4v.

Ryobi 40v battery models indicate battery capacity

You've probably noticed this already, but the battery models reveal the battery capacity. Ryobi batteries whose model number begins with "OP40" belong to Ryobi's 40v line. The next two digits indicate the amp-hour rating of the battery. Additional digits or characters indicate a change from earlier revisions of the same capacity battery. So for example, with battery model OP4026 the "26" indicates a 2.6Ah battery. Model OP40261 also indicates a 2.6Ah battery, but the additional "1" at the end suggests a different revision of the battery from the original model "OP4026".