It's duracell batteries I've been using, I don't purchase anything else. The graphs on the link were interesting.
Eventually, I will order the Ultimate Zapper but for now I will continue with my zapper, only had it six weeks. It's doing the job but I'm thinking long-term and want constant discharge. I know I'm wasting battery life by discarding them after a few days but I just want to make sure I'm getting the proper discharge by changing regularly. It's costly, each battery is about £3.50 here!!