Nistelboy

Hi all, I'm new to this forum but not particularly new to astronomy. Anyway, I have an issue and I'm hoping that there is someone here who can help or at least point me in the right direction. I have a celestron advanced VX which I have now owned for probably 5 years or so, I lost a bit of interest in astronomy so all of my equipment went away and I have just recently started it all up again. Iwas powering the mount using an RAC heavy duty jump starter, which, admittedly, I haven't been keeping on charge! So there is a fair chance it is dead/on it's way out. So I purchased a talentcell 8300 from Amazon, it arrived today (12th) and I plugged in straight in to the mains to charge up, as soon as it was fully charged I plugged it in to my mount and nothing, literally nothing at all, no lights, no reponse, it's as if I had not plugged it in. So I plugged one of my RAC units in, one of them, when fully charged, will power the mount but not fully, the power LED comes on but the backlight on the HC does not and all I can see on the display is "boot start". I then tried to power the mount via the same 12v cable as I was using from the RAC units but with the power pack plugged in a charging too, this all worked exactly as expected, everything turned on, I can input into the HC and the motors all respond to input. I have noticed that the power LED on the 12v cigarette connector does dim dramatically as soon as I turn the avx on (when plugged in to the RAC pack). I purchased the talentcell unit as I had noticed on other forums that people were using it for the same mount, it is rated as 12v and 6A output so all should be ok. I have not had a chance to check anything with my multimeter, and, honestly, I'm not that handy with one! Any help would be greatly appreciated Many thanks