Yup
Wrong
Sorry
It’s ah/a=h
Amp hours divided by amps = hours
So your example would be
10/8=1.25 hrs
Sorry, but I just checked online to find the formula I mentioned, and it is:
The formula is 10 x battery capacity in Amp hours divided by load power (device power draw).
So a 12v 9ah battery and a 10.5 W fish finder would be 10 x 9 / 10.5 or 8.5 hours.
(kind of a "right church, wrong pew" scenario)