Having run a battery shop that sold reconditioned batteries, here is the poop.
We would purchase the battery cores from all the local Kmart, Sears, and Walmart stores for a dollar over core cost, which is usually about $2 per battery. That includes free pickup. We would then take these batteries and do a quick voltage check. Anything below 9volts would go to the recycler. The better batteries would go into rows of 20 connected in series to a charger. We would often have 200 or more batteries charging each night in our warehouse. After charging, we would let them sit for 24 hours to cool. Then we would test each battery with a load tester. We would easily get 60 to 70 percent, test good batteries. We then take these good batteries, spray paint them black, put on a battery label, and clean the terminals. When done, the battery looks almost like new. We would leave them on consignment at gas stations, car washes, tow lots, car lots, and other places. Then come back in 30 days, to collect our money and leave more batteries. We would warrant the batteries for 30 days. How much would we sell these batteries for? For light duty batteries $24.95 and heavy duty batteries $34.95. We easily sold 4 or 5 hundred of these batteries a month.
You would be surprised at how many people would purchase a new battery when they really didn't need one. To be exact - about 60 to 70 percent of the people!