Sorry, can't add much except I have the same problem with the Logitech K340 keyboard under LMDE UP7. The battery level of the corresponding mouse is read correctly.
Interesting enough, SolydX (with Gnome) reads the both mouse and keyboard levels correctly. Must be some subtle difference.
Dell Latitude E6230 with Intel i7, 8GB RAM, 500 GB SSD
dual boot: LMDE and SolydX both running gnome-shell 3.8
surviving in a Windows world with VMware WS 10 and Crossover 13