First of all, the safety voltage of lithium batteries is 2.4V to 4.2V, but generally lithium batteries have almost zero capacity at 3V, and the voltage drops quickly during the 'use ; the working platform voltage of lithium batteries is also 3.65; for Grade A batteries on the market. V (expensive manufacturers basically charge 7-8 yuan per Ah), and the B-grade platform can be around 3.5V. So the 7.2V voltage you designed is low and the power you use is only 55-65% at most. Let's just assume you used 65%, 12W*30H = 360W 360W/3.65V = 98.63Ah then 98.63A/65% = 151.738Ah = 151738mAh. It is recommended to set the low voltage to 6 V.
Let me talk about using lithium iron batteries! The lithium iron battery platform voltage is 3.2V, but generally only 3.1V; LThe maximum voltage can reach 3.9V, but 3.65V is already fully charged and the voltage will drop to 3.45V when fully charged. Advantages of lithium iron batteries: stable platform, high power, stronger temperature resistance than other lithium batteries and environmentally friendly disadvantages: poor consistency, prone to mismatch when used in series, and some batteries are likely to appear if no protection panel is present; Charging too high will result in faulty batteries; if a protective panel is added, this will happen easily. If the voltage of a certain battery is too high, it will be charged in advance and protected, preventing the other battery from doing so. be fully charged, thereby reducing capacity throughout the day. Recommendation: Use a lithium iron phosphate battery and a charge equalizer! The tension of two bateries can be charged and balanced. I'm a lithium battery engineer!