Same brand, different battery
STIHL also sells STIHL AS and STIHL AP. We have no source saying their packs fit STIHL AK tools, so don't assume a shared brand means a shared battery.
The STIHL AK lineup
STIHL AK is STIHL's cordless battery platform. PowerToolGrid lists 21 products in it: 4 batteries, 3 lawn mowers, 4 string trimmers, 2 leaf blowers and more. Prices on file run from $106.99 to $449.99.