Is your Game Boy Advance CleanJuice battery mod hissing or getting hot? Is your board draining battery when it's not in play?
Hissing is normal when capacitors charge on initial installation. Your battery and PCB should not get hot. If you hear a sound coming from your battery, it is most likely faulty and should be replaced.
At any point, do not continue to charge batteries that continue to hiss or get hot to the touch over time. Normal warming occurs during use for a longer period of time.
Check out this video for a more detailed look at the module and troubleshooting it.