My take: Sizing is a margin problem wearing arithmetic's clothes — the formula is two
lines, and the failures are almost always the depth-of-discharge or autonomy decision that was skipped
to save money, paid back in early replacement.
Why: The arithmetic gives a floor; the margins give the design. A bank built on the
usable window, the worst-case gap between charges, and a glance at the load's peaks matches its math
in year three as well as day one — which is the actual definition of the right size.
My editorial view, not a purchasing guarantee.
Frequently asked questions
How do I size a battery bank?
Multiply the load in watts by the hours needed, divide by the system voltage, then divide by the usable
depth of discharge. 100 W for 8 hours is 800 Wh; at 12V with a 50% lead-acid window that is about 133 Ah.
Should I add extra capacity for cloudy days?
Yes — autonomy days multiply the bank. Each extra day of backup doubles the rated capacity, so decide the
worst-case gap between charges before sizing, not after.
