One of the advantages of micro-hydro is that the power just keeps on keeping on. Batteries are kept up to snuff all the time, but in the event that something, like frazil ice, stops it from spinning, suddenly the batteries mattered.
In the beginning all I had were a couple old car batteries and as long as the amps were continuously being spit out of the spinney thing, they were good enough. However, when the little genny stopped the batteries only held enough of a charge to keep the lights on for an hour at best. Soooo, the solution was better batteries, and good deep cycle Voltaire’s piles aren’t cheap. This was way before lithium ion was common, so I searched for the best ones I could find. My good friend and hydro guru told me that the Rolls Surettes were the top of the line, so I dug the money out of the jar and took the plunge. At $700CDN each, I bought 4, which gave me 450 AH of storage, good for about 8 hours if the system went down.
Another thing about a DC system is that the batteries are like a buffer when I draw a heavy load like my table saw or the toaster. Of course, having a big enough inverter is important too, but that’s for another post.