where to buy cell phone battery?

You have not mentioned the make of the phone and place where you reside that will make it a bit difficult to answer your question exactly with the information you need. Coming back to your question, you would have bought the battery from an unauthorised reseller and there are chances that he may have sold you a local battery which looks like the same as original one which you got with your cell phone. Using a local battery can cause damage to your cell phone plus it will not give you the backup time an original battery does. Generally an original battery purchased from an authorised reseller comes with a warranty period of 6 months , in some cases it can be upto 1 year also depending upon the manufacturer of your cell phone. Original batteries can cost a bit higher than the local cheap ones but they make sure that your cell phone is free from any damage and if it doesnt give proper backup than you can ask for a replacement for the same directly from the manufacturer by just showing the original bill of the purchase. So always keep the bill safe because it will be needed if you want a replacement for the battery. Always buy original accessories from Authorised shops because they come with a warranty period and it will be easy to replace them if they start having any prooblem. hope the answer helps.