I can't see Musk trying to build a battery company as his primary focus. That's not exactly a world-changing life goal (well, for him. I'd be happy with that). That's like saying that Apple is a chip company because their chips are central to efficiency.
The battery might currently be the most important single component of an EV, but there is no guarantee that will be true in five/ten/twenty years. The car is more than just a mechanism to increase scale. You don't beat Musk by making a better battery company. You'd better find a way to beat this:
(The word 'battery' is not even mentioned in the article. Tesla could have less battery life but still win.)
Again, similar to Apple, Tesla found a point of advantage and will own it. The landscape will change and so will Tesla's efforts at building or maintaining an advantage against some very powerful companies.
Batteries may appear quite humble, but they are at the core of just about every technological advancement we have at the minute. Cars, laptops, phones, wearable devices.. they all depend on batteries. At the minute battery life is a real bottleneck for us. We are turning into a nation that plans their life around moving from charging station to charging station. Batteries are heavy and they don't last that long. The next truly world changing advancement is going to have to involve making access to energy much less heavy.
I have no idea if batteries are Musk's primary focus here, but creating very cheap and dense storage for electricity WOULD be as world-changing as you can get: if you solve that problem, you can't just replace combustion engines in cars, you can also use solar and wind power for base load on the grid.
This would be much more world-changing than cheap rockets.
"The danger of AI is that is will put increasing power in the hands of those who have the data and the know-how, i.e. large corporations and governments."
This assumes AI that continues to serve corporations and governments without question, despite increasing approximations of intelligence. Can you guarantee that?
It's like tasking monkeys to create rules that humans can't escape from. I'd bet on the humans. We can't even create financial rules that we can't evade. The risk in any complex system is emergent, unintended consequence.