hi ziyad,
Main tank, say the averaged current drawn from the 12v battery is 5.3A.
So at 100% eff, a 25AHr battery should work for about 4.5 hours.

If you ran the 81W motor on its own 25AHr battery, assuming a current ratio of 0.66 [for both motors] would give a current drain of

about 3.5A. So a 25AHr battery would last about 7 hours.

Second tank, say averaged 2amps total, if you used a 25AHr battery, gives about 24 hours.
Run the main tank 38W motor [1.8A] and the second tank load [ 2A] from a second 25AHr battery.

Gives approx, 25AHr / 3.8A = 6.5 hours.

This should cover the bi-daily Excom 4 hour load shedding period.

Recharge at 4 Amps, over a 24 hr period 96Ahr at 100% eff, allow 60%,,, gives 58AHr.

Hope you can follow this OK.

Basically what I am saying is reconfigure the main/second tank loads in order to share the load current, if possible.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
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Bill's: www.blueroomelectronics.com/