Planes engines are forever. Batteries are not.
A friend of mine recently gave me 2 planes that were hanging in  his wall as decoration for 10 years. They were in the pool porch, no A/C. The unforgiving Fl sun hitting them for 7-8 hrs a day. One was an OS 46 the other a .5 super tigre.
Well they are both running, or should I say flying. Im not going to lie, it took a couple of days of oil, running iddle, adjusting the low and high needles.
As for the batteries I tossed them both and bought new ones.
The receivers were old 72Mhz so I bought JRs for my Dx6i.
Welcome back to the addiction