There’s no universal cordless power tool battery – why?

Yes, pretty much. A lot of people don't realize this and have no reason to assume otherwise.

Let's say you can lift up to 50 pounds, and your friend can lift up to 100 pounds. You are both tasked with moving a pile of 5 pound weights from one spot to another.

You can move (50) 5 lb weights before getting tired, your friend has the energy to move (100). So, you have the energy to move 250 lbs, and your friend 500 lbs.

However, increase the load to 40 pounds. 45 pounds. 49 pounds. If your friend can move 10 49 pound weights before tiring, are you going to be able to move 5? The work being done is 50% of their max effort, but 99% of your max effort. You might give up after 2 despite technically starting with the energy to move 5.

But ultimately they want that control to further their own self interest.

Of course. But given many of the questions I've fielded over the years, consumer education and expectations will be a considerable challenge.

A common battery interface wouldn't be enough - if even possible at this point; there would also have be industry standards in how tools and batteries are characterized.

A brand has wire strippers on the shelf at Home Depot year-round, and they're made in Taiwan. When they ship promo displays with high volume count of pliers for the winter holidays, the wire strippers are made in China. I bought both, and found the ones made in China to be slightly better quality. Cost could be a consideration, but there's logistics involved with shipping a couple of dozen tools per store x 2000 stores plus online distribution.

I wouldn't be surprised if batteries could be sourced depending on production volume or manufacturing location of the tools they're bundled with in kits.

Cell availability is also an issue. Festool is discontinuing their 5.2Ah battery and replacing with a 5.0Ah battery. I cannot find either in stock anywhere right now. The slight change will give Festool the flexibility to source 2.5Ah or 2.6Ah batteries. It's better to build a 5.2Ah battery that's labeled as 5.0Ah, rather than sell a 5.2Ah battery that only has 5.0Ah capacity.

A couple of brands have had issues with 5S3P batteries not fitting tools that weren't designed for them. Milwaukee, for example, replaced the battery bays of some of their lights when their first 15-batteries came out. I don't think Ryobi ever offered similar.

If Ryobi had new tools that wouldn't fit their larger 6Ah battery, that would be bad.

In my example, I was referencing 6Ah batteries with 3Ah 18650 cells that have higher internal resistance compared to 2Ah and 2.5Ah cells.

Datasheets are tricky.

If I recall correctly, when Milwaukee launched their 5S3P M18 9Ah HD battery, the best 3Ah 18650 cells were rated to top out at 15A continuous discharge current. The best 2Ah cells were rated at 22A. So why would a 5S3P battery with 3Ah cells be any better than a 5S2P battery with 2Ah cells?

I asked the product team exactly this and they mentioned that data sheets are a good starting point, but don't directly dictate real-world performance. What it comes down to is cooling. That, and batteries are regulated so that tool power and performance is comparable across different battery sizes or types of batteries.

Batteries would need to be characterized in terms of max power delivery at a rated temperature. This is very hard to do at high loads, given the cost of test equipment and safety precautions.

Tools would need to be rated as well, something that isn't done at all right now.

I attempted to do that once, but found that maximum power draw depended on the application and work material, type and sharpness of the accessory used, and depending on the tool the type of battery it was paired with.

Look online to see how much dislike there is for the UWO (unit Watts out) unit that Dewalt uses to describe their cordless drills and select other tools. In theory, this is a better measurement for comparing how one drill might perform compared to another, taking into account both speed and torque. In reality, everyone simply wants to know the max torque specs.

I'm not saying it's good to have to buy different brands' proprietary batteries to power their tools, but that - even if possible - a universal battery system will be consumer-unfriendly in other ways.

I really hope I'm wrong.

You cannot just connect + to + and - to -.

What could work is a battery with a new standardized interface, and modular adapters that can match different brands' tool interfaces.

Over the years, maybe some brands might develop tools that mate directly to the universal battery.

But now there are 18V/20V Max, 24V Max, 36V/40V Max, and 54V/60V Max cordless systems. There's no practical solution for this.