EDF speed and throttle issue

[Flying_Fast74]

I have made foam board RC F-18 super hornet following Ben Harber's plans. I am using parts listed below. The issue I have is - After connecting the battery, when I increase the throttle on transmitter, the edfs speed up and reach to only about 80% max speed before max throttle position and then slow down to 30-40% of max speed when I shift to max throttle position. If I were to immidietly push the throttle to max speed instead of gradually, the EDFs will go to max speed, but stay at that speed only for a few seconds and then slow down to about 30-40% of max speed. In each subsequent tests with the battery still connected, the EDFs reach their highest speed about 10-20% slower than the time before. E.g. if I reconnect the battery and EDFs go to 80% max speed before slowing down to around 40%, then the next tests it will reach only upto 45% max speed, and then slow down to 30% of max speed, so on and so forth. Once the speed dips to or below that 30-40% mark, the speed remains constant irrespective of the throttle position. My battery is fully charged (though, I would welcome suggestion of a battery level tester). I want to make sure the edf speed gradually increases and reaches the highest at the full throttle position in repeated tests. I have used one ESC for each EDF. Both of my ESCs are connected to one battery, and are calibrated as well.

Connected parts list:
1) TWO Powerfun EDF 50mm 11 Blades Ducted Fan with RC Brushless Motor 4300KV (Balance Tested for EDF 4S RC Jet Airplane).
2) TWO ZTW Beatles Series 50A 60A Brushless ESC with BEC for RC Airplane 4S 6S (Beatles 60A ESC with Connector)
3) 3.5mm Banana Gold Bullet Connector Extension Cable for RC Brushless Motor ESC Extension Cable Wire (16AWG 30CM).
4) Flysky FS-i6 radio transmitter and FS-iA10B 4.0-6.5V/DC 2.4GHz 10 channel receiver.
5) OVONIC AIR 3000 50c mAh battery. 11.1V (Main Battery for ESCs)
6) ONE Blomiky 8.14Wh 7.4V 1100mAh 35C Li-ion-Po Battery with JST Plug (For External BEC)
7) BW RC Servo BEC UBEC 3A 5V Airplane Receiver Servo Power Supply
8) Onkuey T Plug Male to 2 T Plug Female Parallel Battery Connector Cable (120mm)

[kallend]

1. What happens if, after a test where it slowed down, you close the throttle and leave it closed for, say. 2 minutes while leaving the battery connected, so the ESC can cool down, and then open the throttle again?

2. Do you have a voltmeter you can use to test the pack voltage when under load? Or pack voltage telemetry on your radio?

[Gilatrout]

Does your charger show Internal Resistance? These symptoms strongly suggest a bad battery due to high IR.

[kallend]

Does your charger show Internal Resistance? These symptoms strongly suggest a bad battery due to high IR.

Agree, but the problem only seems to manifest itself under heavy loads and may not be apparent in an IR test on a charger. Swapping out the pack for a known good one would be an easy test.