Accu will not charge

Dear Sirs, 

I bought a transmitter accu two years ago, but I never used it untill now, but when I tried to charge it the charger, also bought from you, tells me that charging fails. I forgot the message stated, but I can tell you this later as the accu is with the boat in a local Boat Show right now

The details of my order is so:

HobbyKing 1500mAH LiFe 3S 9.9v Transmitter Pack.

ORDER #100350911

Order Date: March 14, 2017

I know that I do not have any right of warranty, but I would kindly ask what can be wrong? Can it really be so that an accu do so when never used? It still have plenty of power in it, close to new, but stlll?

Kind Regards

Steffen Hansen

Denmark