The caps don’t contain anything. The issue with earlier caps is the inside diameter is slightly too small and the battery can’t move around in them. This means the battery doesn’t get pushed freely by the spring and has a poor contact with the terminal at the other end of the chamber. The inside diameter of the newer version of caps (they say v3 on them) are ever so slightly bigger, allowing the battery to move freely.
Source: Me. I had constant drop outs and sometimes not even turning on. Powertap sent new caps for free and it fixed it immediately.
But another problem is that they go to sleep way too quickly if you’ve stopped for a few minutes or sitting on the line before a race. Make sure you back pedal every minute or so to keep them awake. Sometimes they won’t wake up until you’re going and then actually stop peddling for them to become active. It’s weird and annoying.