The AH rating is how many amps can flow through (out of) a full battery before it is dead.
In series, All the amps flow through All the batteries.
Twenty 12V 140AH is still 140AH, but a 240V 140AH.
And 240V x 140AH = 33.6KWH of power.
Twenty 12V 140AH in parallel is still 12V, but 2800AH.
And 12V x 2800AH = 33.6KWH of power.
Batteries hold a fixed quantity of power. 12V x 140AH = 1680WH.
And 20 hold 1680WH x 20 = 33.6KWH.
They can be arranged to different voltages, but the "power" is the same.
Draw out half, at the 10 hour rate, is half the rated 10 hour amps.
The 10 hour drain for 'dead' is 14A. (140AH / 10H = 14A)
Half is 7A.
That ignores the Peukert effect, temperature, etc. But 7A is close enough!
G-