I have piggy back shocks on my banshee and they seem to have gone flat. Can you put air in the resevoir and if so how much?

 

Your seals are blown, shocks need to be rebuilt or replaced, and it is not air for the shocks, but Nitrogen, it is dry and clean, and you are looking at 120 psi or better charge on some shocks, so do NOT mess with that "air" fitting on rez. take it to a shop to be looked at. Probably no Nitrogen left, if shocks are sagging.

 

Yup, take them to a shop for a rebuild. Don't even mess with trying to put air in them.