title_body: How to restore LiPo-powered aircraft that have not been flown for years? I have a bunch of relatively inexpensive battery-powered radio-controlled aircraft that I haven't flown in over a year.  I haven't flown some of them in over 3 years.
  
  The aircraft are airplanes, helicopters, and drones.
  
  I believe they are all powered by LiPo batteries that are designed to be recharged, not replaced.
  
  From what I've learned about LiPo batteries, they tend to go bad if not used for a long duration.
  
  What general steps do I take to resurrect all these aircraft so I can fly them again?
upvoted_answer: You may need new batteries.
  
  When a LiPo battery fully discharges, thin whiskers of lithium metal form between the plates of the battery.  Attempting to recharge the battery will cause these whiskers to overheat, which may cause the battery to catch fire or explode.
  
  Commercial batteries from reputable manufacturers have self-monitoring circuitry that will permanently disable the battery if the charge level drops too low.  If the batteries are of this sort, it's safe to test them by recharging -- if the battery has been damaged by over-discharge, it simply won't take a charge.
  
  Cheap third-party batteries and homemade battery packs don't have this protection.  A battery that's only been sitting for a year may still be good -- I'd try recharging it in the middle of a concrete driveway or some other well-ventilated, fireproof location.  With a battery that's been sitting for three years, I wouldn't risk it.