title_body: Methodology and sources for obtaining the correct replacement batteries for low-end RC aircraft According to Mark's answer to this Drones and Model Aircraft SE question, I likely need to buy quite a few replacement LiPo batteries.
  
  Finding large LiPo batteries for expensive aircraft is usually rather simple.  There are scores of websites that sell them, as well as many brick-and-mortar RC/hobby stores.  Standards exist to help guide one's purchases.
  
  But for the small "non-replaceable" batteries that are included in inexpensive RC aircraft, what are some good sources?  By "non-replaceable", I mean that the batteries are not designed to be replaced, but, of course, can be replaced by someone experienced with electronics and aware of the required safety protocols.
  
  What methodology is appropriate for getting the right battery for each aircraft?
upvoted_answer: Most low-end aircraft use small LiPo batteries (lithium polymer batteries). If you want to find a replacement battery you can look at the voltage and capacity of the original battery and purchase a similar one. For example, if the low-end aircraft used a 100mah, 3.7v LiPo battery, you could go to anywhere that sells various batteries such as Amazon or hobby shops such as RaceDayQuads and buy a battery that is similar. You should buy a battery with the same voltage and the same capacity. You can also buy a slightly (but not much) higher capacity battery for longer flight time. Also, know that different LiPo batteries may be better or worse. Cheap batteries may be low quality and not last long or cause fires while more expensive ones tend to last longer and perform better.