I am using 5 cell Zippy compacts, two packs in series. I bought the first 4 packs last year. When I was preparing them with connectors and Velcro, I noticed one of three packs was 1/8" narrower than the other 3. It also had a cell with much higher internal resistance. I made no attempt to return it, I purchased a replacement pack. I purchased another set of 4 packs this year and they were OK, but it looks like you need to check them carefully when you get them.