If you're getting 50% productivity, something's not right.
The productivity of the charging recipe for the Electromagnetic science packs should be locked at 0%, and on my side, it's working as intended. While the productivity bar shows up (I still don't really know how to hide it or make it go away), I don't get more packs by charging them, and i can't put productivity modules in the EM Plant (as expected).
Maybe you're using other mods that change stats for the EM science packs; that might be causing your problem.
Or you might have been tricked by the prod bar showing up ?
If you have any ideas for getting rid of the bar, I can try to implement a fix :)
Otherwise, tell me your mod list so I can check for weird compats.