I saw a Computer mag article a while back that tested about 6 diiferent makes of AA batteries and it was some Tescos own brand that came out tops. I think the mag was Computeractive. Duracell came in second. From what I remember the Tescos lasted about 100 hours and the Duracells about 96 hours. I cant recall exactly what the test was but it was identical for all the batteries and as you can see it was pretty close. My Logitech mouse uses 2 AA's and i have tried all sorts but Duracell wins hands down every time On average they last 3 months and others that i have used last around 6 weeks.