So, this is so easy to fix if you are willing to be a little handy dandy.
Note, if you are using US Duracell batteries they changed the size and these thiccc boiz are why this thing "breaks". Forcing the large batteries in, will bend the metal pieces that complete the circuit out of alignment the more you use it. Go for some dollar store batteries, they are the original size and actually fit in the darn thing smoothly.
I'll do my best to explain this without pictures.
All you have to do is open it with a small Philips head **** driver, and bend the longer, top most, metal piece on the half with the back plate up slightly. This way there is a better chance of it connecting when you press the button.
When reassembling, be sure to align the long piece you just bent in the gap below the button pressing plate. Also, align the motor and springs correctly below their battery plates. The shorter spring goes under the battery plate on the half with the button, and the longer spring goes under the half with the back cover.
Essentially, when you press the button at the top of the mixer down, it will press the longer piece down into the battery plate, and then also press down into the shorter spring, completing the circuit.
Honestly, this is easer than fixing a videogame controller. I was originally worried that it was broken due to water damage.