Given that the Medion Akoya Mini is pretty much the same computer as the MSI Wind, this news should come as no surprise. MSI has been saying since June 16th that it would be shipping the lower capacity battery due to a global battery shortage.
Both MSI and Medion say that they will make 6 cell batteries available at a later date. But computer makers have a tendency to charge an arm and a leg for spare batteries, so if you want an extended battery your best bet is usually to buy one when you buy your computer. Unfortunately, that doesn’t appear to be an option at the moment.
There is a silver lining here. Both computers are built around the new Intel Atom CPU, which provides decent performance (for a cheap ultraportable) while consuming very little energy. If you can expect 5 hours of battery life from a 6 cell battery, it stands to reason that you should be able to get about 2.5 hours out of a 3 cell battery, which is not bad. Not great, but not bad.