Unusual ESC problem, not remembering throttle range setting

[Old School]

I have a Turnigy Marine 150 amp ESC (purchased several years ago but never powered up until yesterday) that when I connect to the battery will beep constantly (Xmitter is already powered). I set the throttle range as described in the instructions by switching on the Xmitter, applying full throttle and then connect the ESC to the battery and get the "beep-beep". I release the throttle to zero within the five seconds and I get the four beeps indicating that I have 4s power. The ESC then will run fine. Moments later after depowering the system and reconnecting power the ESC remembers its throttle setting and will work. However, leave it for a few hours and then connect power and I have to go through the throttle range procedure again. It seems that the ESC has no memory retention of the throttle setting. Any thoughts, please.

[Old School]

As a followup this morning, 24 hours since the ESC failed on startup as it had the day before (giving continuous beeping sound), the unit fired up normally giving me the four beeps for 4s and then functioned as per normal. I cannot say if it has corrected itself or perhaps just being temperamental.

[srislash]

Now it has been awhile but I remember something about turning Tx off first For the calibration to take, or maybe the other way around, like I said it has been awhile

[Old School]

Many thanks, next time it happens I will turn off the Xmitter first and see if it retains the memory.