Replacement non-original batteries are mostly junk (not just for Nokia, for all devices using brand-name lithium ion batteries). Due to the total lack of standards, testing, or reliable ratings, suppliers are free to put whatever rating they want on a barely-functional battery made as cheaply as possible, with the expected results. Given the huge disparity in cost between original brand-name batteries and replacements, it may still be worth experimenting. But until we see some reliable standards, your chances of finding a good replacement battery at random are pretty slim.