This is interesting.
I have a BOSS WL50 and it works perfectly with every active instrument I have hooked up to it. They all have the common TRS jack with the battery on the R.
However, I have never tried it with my El Toro, which has a really wacky and complicated output jack. I assume it's shorting the battery to the R.
I'll try it out with the BOSS and see what happens and report back here. Better to know now, before I show up to play...