There's an additional part which is crucial: No DRM-crap (secret APIs, cryptographic handshakes) preventing other companies from selling safe replacements for the original Sealed Danger Boxes.
The price winners will be deadly unsafe replacements, and I can 100% see why you wouldn't want to open yourself to that kind of liability. It only does so much good to find out in court that a random no-name battery caused a fire after your brand gets dragged through the mud for burning down someone's house (and you can't bring their house back either)
There are already epidemics of battery fires in major cities of shoddy no-name bikes because of batteries specifically, there's no way those companies should be allowed to infect the market outside of their own bikes too.
I'd test that idea by checking if it fits broadly across other industries and products. For example, do you feel the same way about brakes in cars and power-supply units in computers?
Would you accept a company like Ford or Lenovo using the "our branding is more important than your property" logic when forcing you to buy parts from themselves and literally nobody else, no matter how well-regarded the third-party parts are?
The problem is, we have reasonably tight control on a lot of other safety-critical supply chains where the only way to get cheaper is to be straight up unsafe. That's why your brake pads don't need DRM.
But the horse is out of the barn on batteries. For a myriad of reasons, lithium ion batteries just somehow flew under the radar long enough that now literal boatloads of fire hazards are landing daily and no one has been able to stem the problem.
Thermal sensors can only do so much for a bad battery design if they're on the bike rather than the battery, this isn't an engineering problem, but the closest thing to an engineering solution is to completely disincentivize 3rd parties from making batteries over a certain size as far as your own product goes.
What I mean is that with a rigorous check any battery no having a CE mark (here in Europe) or other type of certification then it can’t be imported. I believe there is a world where reputable battery brands make all sort of battery for Ebikes, vacuum cleaners etc that fit the device and have an appropriate mark. No need to have a price tag like the bike manufacturer just a plain good battery maker.