Can you recommend where I can get a reliable replacement battery?

@tonnika that will depend entirely on where you are located. As a rule of thumb I stay away from most sellers on ebay, aliexpress, amazon. Yes, there are probably reliable sellers on there but there are more unreliable ones. Personally I prefer injured gadgets, iFixit, Newpower99 etc.since I have purchased from them. Ultimately this is not a objective answer just my preference. Pick a vendor that appeals to you, and contact them. Get a feel for their customer service and ask questions regarding guarantees, returns etc. see how and if they answer.