My only quibble with this Battery Pack is that it does not comfortably fit into the Magic Mouse, hence the 4* awarded. I've tried every way to get the 'pack' it 'locked' in to the mouse, but this has proved impossible. Having said that, the pack works well. We now have two such packs plus the one charger and we alternate the charging as and when required. Both packs hold the charge well. Although only awarded 4*, I'd still say that this is an excellent product overall.