I just partially read a post on a guys F-16 going in and the MPI MK 3 regulator was mentioned. It was discussed it was used as a battery back up etc.
I did not read the entire post due to it being too long. My intrest peaked on the regulator.

This regulator is NOT a battery back up. The 2 packs have to be the same exact packs with the same charge. The regulator uses both batteries at once. Not like a battery back up with 2 seperate switches that will use the strongest pack first.

I could go on and on but this info is from Troy Built models web sight at this products page.

Accessories/regulators.

This probably didnt cause the F-16 trouble . I just wanted to spread the word. This info MAY be incorrect if Toy Built is wrong. I bought one for my 35% YAK and when I got it. This warning was with it. I never used it.