Checking the current draw would probably not help much since zinc air batteries are really like fuel cells. Once the tab is pulled, allowing air to get into the battery, a chemical reaction starts that cannot easily be stopped. This reaction runs, producing electricity, until the battery is depleted.
For a given environment (same temperature & humidity), the battery lasts about the same length of time whether or not there is a current drain on it. You can oull the tab and not use the battery and it will still deplete in the same length of time.
Referring to the posted datasheet, here’s some calcs using a spreadsheet
zinc air 312
130 =mAh capacity
6 =how many days
16 =how many hrs/day
96 = total hrs
current draw
to get these many hours is
1.354166667 =mA = mAh/hrs
rounded to two significant figures this is 1.4 mA.
for
25 =hrs
you’d need to draw
5.2 =mA
And mAh = hrs x mA and hrs = mAh/mA
There are several unknowns:
what mAh usage can the typical customer (50th percentile) and the worst case customer (95% percentile) expect from the aid?
how much does self-discharge contribute to this? Trying a different cell technology may help answer this question.
what mAh rating does the cell typically provide at the current draw of the aid? Cell capacity varies somewhat with discharge rate.