The iPad mini 5 has been scheduled to be released in 2017. The housing of this tablet is a lot thinner than the others that had come before. Because it is thinner, it will have a smaller battery. This doesn't mean because it has a smaller battery performance will suffer. This battery that will be installed will have the same strength as it's previous forerunners. The housing of this tablet will use the same 7000 series aluminum chassis that was used for the iPhone 6.
There are rumors coming out that the the iPad mini 5 will also be dust resistant and waterproof. Most probably, the newest iPad mini 5 will be introduced in 32 GB, 64 GB and 128 GB in the 2nd or late 3rd quarter of next year. Who knows, it might come out even in March 2017.