There's a very large difference between using batteries as an intermediate point and temporary storage point for input into the grid, and using them as a primary power source for datacenters, which are one of the most energy intensive operations around. The longer you need to store power, the less economically viable battery use is. Even if you had enough perfectly consistent (hah!) solar/wind generation nearby to power your facility, the battery levels required to keep the facility powered would be prohibitive.

I am a network engineer who works in both larger datacenters and smaller network closets/hubs, and even the battery backup required to keep a single crowded vertical network rack running for a few hours in the event of a power outage is hundreds of pounds and waist high. Scaling that out to large datacenter levels of power consumption and overnight capacity and you're talking completely absurd levels of expensive power storage capability.

And again, if there's a good location for a cheap and green new power installation, it's not really to Microsoft's benefit to get into the power business. It's 100% going to be cheaper for Microsoft to let someone else build and run a power plant that feeds into the general grid and just take advantage of the lower aggregate power cost.