As a preface, I am a experienced and heavy mobile phone users. I have had a mobile for nearly 6 years now, and I have had 4 services, and 5 different phones. I love the Nokia 5100/6100 line of phones, and this battery fits those.This battery is amazing. It is way too light, and way too small (these are good things.) I really believe that this is more than enough power for the average mobile phone user who charges their phone every evening. And any user would be impressed with it's size and weight, it is a great unit. However, I must say - for me, it is not quite enough power. I should have known better as it is only 750 mAh, but I wanted something thinner. I use about 2500 minutes a month on my phone, so you get the idea about my ussage patterns. It does last all the way through MOST days for me, but those few days it doesn't that is a problem. If your use 1500-2000 minutes or less, this is probably the greatest batter you could ever own. My plan now is to get this companies 2100 mAh version of this battery for my everyday life and travelling (where I might not charge every night), and keep this amazing small one for my evenings, where less weight in the pocket is very handy. I do highly recomended this battery as it does everything it advertises, and more. Just be aware if you are an extremely heavy user.