Lead acid batteries are 85% to 95% efficient. A good AGM is 98% efficient. As a data point, I sized the batteries at my cabin to provide two days of power unde

Lead acid batteries are 85% to 95% efficient. A good AGM is 98% efficient. As a data point, I sized the batteries at my cabin to provide two days of power under total cloud (more than enough for getting to 24 hour solar power) and the batteries cost about half what the panels did. (That discharges the batteries to 60% capacity. You also need to consider that the batteries will last about 6 years then get recycled. I mentioned AGM because they can charge much faster. If you are only interested in 24 power shifting, it might be cheaper since you'd need to buy more capacity in lead acid batteries to tolerate the charge rate. )