Problem with RC helicopter - K11 model made by 'Kaixiang Toys'.?

I bought a K11 model RC helicopter made by Kaixiang Toys (China). They have a website www.kxttoys.com which doesn't even work properly. My RC helicopter flew about three times for about 5-8 minutes each. I used the provided charger (Shantou Huajun Electronic Co. Ltd AC/DC Adaptor. Model: HJ-AU-036450 . Input: AC230-240V 50HZ, Output: DC 3.6V 450mA) which has a two pin JST socket. The socket has two male pins. This socket then connects to the battery onboard the helicopter - a 3.7V 500mAh lithium polymer battery that has a JST 2-pin port. I had the charger connected to the helicopter for around 60-90 minutes as instructed in the manual.
The fourth time I tried to fly it, it just had enough power to spin the rotors and then stop. The next day I turned the power switch on and off on the helicopter and absolutely no power at all. Not even to light the LEDS.
I tried charging it again and nothing. I noticed that when the charger is plugged in, it does not get warm, like other chargers do, making me suspicious that perhaps the charger is faulty? I removed the battery as well to see if perhaps a wire had burnt out, or come loose. I have since tried charging the battery several times over and connect to the helicopter's JST plug with nothing happening.
I cannot find this charger online (it is listed as part number 338-25). The battery is listed in the manual as well (part number 333-040), which I managed to find on EBay and order.
I bought this helicopter from Paddy’s Markets Sydney Australia for AUD $45, so costly enough to be very annoyed.
BTW it is a 3 channel RC helicopter. The RC unit works and needs 6 x AA batteries to operate.

Hi.
The trouble should be in the battery pack. If one battery is faulty it won't charge.
And if you say that during the night the batteries uncharge, I am sure the trouble is in the battery.
Try to see the voltage when charging? Do you have a voltameter?You 'll see if the charger is good.