I have two usb chargers. If I put the XL on the one charger and charge it, it only gives me about 4-5 hours of use. If I put it on the second charger and charger it, I get 9-10 hours of use. I finally figured out what charger did what and marked them. This does not happen with the shorty battery, it does the same on both chargers.
Also if I put the XL on the charger that does the shorter time, then move it to the other charger the red light comes on and it charges for another 90 minutes or so.