Review on 50 Count GP A23 GP23AE 21/23 23A 23GA MN21 GP23 23AE 12 Volt Alkaline Zero Mercury Batteries by Will Haglund

From my experience with this type of security key battery, they last about 2 years. For window/door sensors, it can take 3-6 months. Because of the way they are made, they are prone to early failure. Inside each of them, no matter whose name it says, is a stack of 10-1.2V button cells. One dies, and he ends up dragging the rest with him. Sometimes there is a particle of dust or grease between one or two, leading to premature failure. I took the stack apart and found 6 still at 1.2v and the other 4 at less than 4v. I've used them from brand name to "never heard of them" and they are all the same. You can't find where they are made in China but I doubt there is more than one factory. Buy the cheapest you can find. This pack of 50 is great because the cost of the pack is so much lower. Check price for two packs. This non-recyclable plastic is expensive!