Are Ryobi 40V batteries compatible with all 40V tools and chargers

Broadly speaking, all 40v batteries are compatible with all 40v tools and chargers. However, some of the newest "tall" batteries may not physically fit in certain older tools. Also, I've found that the OP406A rapid charger simply won't charge certain older, lower capacity batteries.

The most recent of Ryobi's 40v batteries are taller than previous models, probably because they contain THIRTY cells whereas the older batteries contained only TWENTY. As a result, these batteries will not fit any tool which was molded to fit completely around the back of the 40v battery. "Tall" batteries such as the 7.5Ah OP40752 and the 6.0Ah OP40602 will not fit into these tools (and there may be more):

Humorously, the ad for the 7.5Ah battery on The Home Depot's website includes a generic video which pitches the 40v system and which depicts two tools which are incompatible with the 7.5Ah battery due to the battery's extended height! Look carefully at the video for the mower at about 0:05 and the chainsaw around 0:20.

I do own a Ryobi OP406A Rapid Charger and batteries with capacities ranging from 2.6Ah to 6.0Ah. I've found that the OP406A simply refuses to charge the 2.6Ah batteries, but YMMV. This is fine by me, because IMHO the charge rate of the OP406A charger is so high that IMHO it shouldn't be used with batteries smaller than 6.0Ah anyways.

9Ah and 12Ah batteries are coming?

YES! Check multi-model manual above for the 7.5Ah battery and you'll find that this manual applies to battery models "OP40602/OP40752/OP40902/OP40122". The first of these two refer to the newer 6Ah battery and the 7.5Ah battery. Given the nomenclature, a 9Ah battery and a 12Ah battery are suggested by the latter two models.

Note that the nomenclature of the 12Ah battery is a little confusing when compared with the other models. For all batteries before the 12Ah battery, the two digits representing the battery's capacity were 10x the battery capacity (i.e., 1.5Ah = "15", 2.6Ah = "26", 4.0Ah = "40", 7.5Ah = "75"). But for the 12Ah battery the two digits used are "12", even though "12" might suggest a 1.2Ah battery.

Update 27-Mar-2022: The ryobitools website now shows 8Ah and 12Ah batteries coming soon, but does not mention a 9Ah battery. It appears that Ryobi has addressed the nomenclature issue by placing an "A" after the battery capacity: OP4012A1 = 12Ah, not OP40122 as shown in the manual.
Think about how much energy is in a Ryobi 40v 12Ah battery! That would be (36v)(12Ah)= 432Wh. To put this into perspective, 20 years ago when Ryobi released the 18v tool line it was powered by 18v NiCD battery packs which contained 15 Sub-C cells rated 1.2v @1.5Ah for a total pack energy of 27Wh. So the 40v 12Ah battery has the same energy capacity as 16 of these 18v batteries!
Consider the typical Group 24 size deep cycle marine battery. I'm talking a big, heavy 45lb battery, typically rated around 70Ah. The total energy in one of these batteries would be (12v)(70Ah)= 840Wh. But most deep cycle marine batteries are built to handle only a 50% depth of discharge. Discharging more than 50% on a regular basis will greatly reduce the battery's lifetime. So that's 420Wh usable energy in that 45lb battery as compared to the full 432Wh capacity of the Ryobi 40v 12Ah battery. Yes, the Ryobi 40v 12Ah battery has roughly the same amount of usable energy as a typical group 24 deep cycle marine battery!

Why would Ryobi release both 20-cell and 30-cell configurations for their 6Ah battery?

You may have noticed in the table above that Ryobi has released at least three models of 6Ah 40v batteries: the 20-cell OP40601 the 30-cell OP40602 (and I'm not sure how many cells in the newest OP40604). The 20-cell battery is the same size as most of the rest of the line including the 4Ah and 5Ah batteries. The 30-cell battery is taller and won't fit in certain older tools. All of these configurations have exactly the same amount of energy, 216Wh. I happen to own two of those older tools which can't be used with the larger 30-cell batteries, so when I last purchased a 6Ah battery I made sure that I picked up a 20-cell configuration. From the manufacture dates that I've seen, it's clear that Ryobi did not simply replace the 20-cell OP40601 with a 30-cell battery. Ryobi is simultaneously manufacturing both 20-cell and 30-cell configurations! But why?
My first theory on this was that it was simply a cost or availability issue. For this to be the case, it must be true that the cost of 2Ah cells are less than 2/3 the cost of 3Ah cells, or that the supply of 2Ah cells is much greater than the supply of 3Ah cells. Either one of these could be true and I have no evidence available to support or challenge these theories.
But it occurred to me that in certain situations (most notably with the big 1600W inverter) the configuration could actually matter. The 30-cell pack contains three parallel strings of 10 cells and the 20-cell pack contains two parallel strings of 10 cells. Both the 2Ah cells and the 3Ah cells are rated with the same continuous discharge rate of 20A. Therefore, three strings of cells in parallel will be rated a continuous discharge rate of 3x20A=60A whereas two strings of cells in parallel will be rated 2x20A=40A continuous.
Does this really matter? For most tools the answer is NO because while many tools may require a short burst of energy exceeding 40A, most tools don't require 40A or more continuously. At full charge these batteries can continuously deliver 42v*60A=2520W or 42v*40A=1680W. Just before these batteries are fully depleted they can continuously deliver 30v*60A=1800W or 30v*40A=1200W.
The 1600W inverter is perhaps the only Ryobi 40v tool which would require a continuous 1600W or more. If we assume an 85% inverter efficiency, then in order to deliver 1600W output from the inverter a battery must supply 1600W/0.85=1882W. The cells in a single 30-cell battery can drive a continuous load of 2520W to 1800W during discharge, so the 30-cell battery could deliver a continuous 1882W throughout all but the last few moments of its discharge. But the cells in a single 20-cell battery can deliver a continuous 1680W to 1200W, so the 20-cell battery cannot deliver a continuous 1882W even when charged to full capacity.
So in theory, a single 30-cell 6Ah battery can be used to drive a Ryobi 1600W inverter with a full load "continuously", whereas a single 20-cell 6Ah battery cannot. This could explain why Ryobi bundles two of their 30-cell 6Ah batteries with their 1600W inverter rather than 20-cell batteries. Let's not forget that these batteries are rated 216Wh. Under the best of circumstances one battery could deliver 1882W for 216Wh/1882W = 0.115 hrs = 6.8 minutes. So in this case "continuously" means up to six minutes. NOTE: This analysis assumes that the battery's internal circuitry permits such a large load, which it may not.
I now have a third theory about why Ryobi has two different 6Ah battery configurations. Ryobi does not manufacture the cells which go into their 40v (and 18v) batteries, they purchase from other manufacturers which until recently included Samsung, LG, and Sony. I've recently read that Ryobi has made the switch to EVE energy and TenPower (see the next section). These alternate manufacturers do not make 18650 cells in capacities above 2.5Ah at this time, so it's not possible to create 20-cell 6Ah batteries with these vendors. All of the other 40v battery capacities are possible with 1.5Ah, 2.0Ah, and 2.5Ah cells, including the larger OP4075 7.5Ah battery (which contains thirty 2.5Ah 18650 cells). However, I'm sure it's only a matter of time before these manufacturers start making 18650 cells in capacities of 3.0Ah (or larger).

Exactly what make and model of 18650 cells are in Ryobi 40v batteries?

I've personally cracked open several different models of Ryobi 40v batteries and each has contained all Samsung or LG cells. IMHO, these are all quality cells. Here's what I've found:

• OP4015 (1.5Ah) contained ten LG model LGDAHB21865 cells. These      "HB2" cells are rated 3.6v, 1.5Ah, and 30A discharge for an      effective 30A discharge rate.

• OP40201 (2.0Ah) contained ten Samsung model INR18650-20R cells. These      cells are rated 3.6v, 2.0Ah, and 22A discharge for an effective 22A      discharge rate.

• OP4026 (2.6Ah) contained twenty Samsung model INR1865-13Q cells.      These cells are rated 3.6v, 1.3Ah, and 15A discharge for an effective 30A      discharge rate.

• OP4050 (5.0Ah) contained twenty LG model LGABHE21865 cells. These      "HE2" cells are rated 3.6v, 2.5Ah, and 20A discharge for an      effective 40A discharge rate.

Furthermore, I wouldn't be surprised to learn that Ryobi uses different cell models with each manufacturing "batch". So for example: I may have found LG cells in my OP4050 5Ah battery, but I wouldn't be surprised if you find Samsung cells in yours.
However, all of the above were found in batteries with date codes from 1Q2019 or earlier. I've read that Ryobi has also used Sony VTC4 cells in some batteries, and I believe these Sony cells to be quality cells. I've also read that Ryobi started switching to Chinese cells in 2020 or possibly as early as late 2019. I found this post on Reddit which offers detailed information on which cells are in which of the newest Ryobi battery models. I cannot confirm or deny the information reported on Reddit, though I suspect it to be credible. The Reddit posting indicates that the newer cells are from EVE energy and TenPower. I have no experience with the cells from these companies. The EVE website lists two "Power Cell" models in the 18650 size: ICR18650/15P = 3.6v, 1.5Ah, 30A discharge; ICR18650/20P = 3.6v, 2.0Ah, 20A discharge. The TenPower website also indicates two 18650 cells: 15SG = 3.6v, 1.5Ah, 30A discharge; 20SG = 3.6v, 2.0Ah, 30A discharge.

Do the serial numbers mean anything?

Yes! All Ryobi 40v batteries (and tools) are stamped with a serial number which includes a date code. The date code indicates when the battery was manufactured. The serial number begins with two letters which I presume identify the factory. The next four digits are the year and week of manufacture, respectively.
Examples:
EU20026N080123 = "20" for 2020 and "02" for week 2
EU18304D230001 = 2018, week 30 = July, 2018
All Ryobi 40v batteries and tools have a 2D barcode on the label which is encoded with the manufacturer part #, serial number, and model #. Here's an example: "130302037DG9|EU20026N080123|OP40601". This barcode indicates manufacturer part # 130302037DG9, serial # EU20026N080123, model # OP40601. The "EU2002" in the serial # indicates that this battery was manufactured in the 2nd week of 2020, or between 06-Jan-2020 and 12-Jan-2020.
Please view the 18v batteries page for good information on Li-Ion battery purchase selection and storage as this information is also relevant to Ryobi's 40v batteries.

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