Gun trouble x2 G&G AK47 & CA M15 SPR

[7heOZ]

Have to interesting problems here that I just cannot figure out

G&G AK47:
I recently acquired one of the Tinted plastic G&G Ak47s and I am not impressed. First it was shipped with a massive crack in the body which was an easy fix, I called the seller and they sent me a new body free of charge. Then I figured out that the battery that came with the gun had a small connecter and the wiring in the stock had a large connector. I then had to take out this section of wiring which included the fuse so I could get to the small connector. After this was all done, I took it out for the day and it performed beautifully. I soon forgave this piece of machinery for all the crap its put me through. All until about 5 hours later...I took a shot on semi and the battery sounded like it was about to die, next shot nothing. Swapped batteries to a fully charged one, still nothing, tried all of my friend's batteries (3) and none worked yet all of the batteries worked perfectly with my friends guns including the one I had used earlier. Any ideas whats gone wrong?

CA M15 SPR:
At first I though this was a battery problem but It seems to do it with all the batteries I try. The first 5-10 shots are fine on full auto but then the rate of fire slows down and eventually the gearbox fails to turn over. I tried an Intelect Small 9.6v 1600mah, an Intellect Large 9.6 3600mah and a G&G 1400mah crane stock battery. Any idea whats wrong?

This gun includes the following upgrades:
Systema m120
Systema Genuine Ratio gear set
Systema Polycarbonate Piston w/ duracon piston head

Thanks in advance guys