So, what's the score with batteries? I bought a 3 standard recently, and I am looking to purchase additional batteries. Thing is, genuine DJI ones appear to be very thin on the ground, with most online vendors (and as of writing, the Official DJI store)  being out of stock. There are plenty of generic batts out there from names I would trust, (EBL, for example), but I am worried about a firmware update making them useless. Are DJI purposefully limiting stock to drive demand and justify the €150 price tag? Have any forum users out there have experience with 3rd party batts?

I wouldn't recommend using third party batteries. I have heard more bad than good. I thought about it too. If you have a best buy near you they almost always have them in stock /or/ can get them in the next day for no additional cost to you.