There are many methods of renewing dry batteries, and I have used several of them, but I found the following the best: Remove the paper cover and with a 1/4-in. drill make about six holes around the side of the zinc, about 1/2 in. from the bottom. Then drill another row of holes about half way up the side and put the battery to soak in a solution of sal ammoniac for 48 hours. Then remove and plug the holes up with hard soap, and replace in the paper box, when it will give nearly as strong a current as when new.