In June I purchased a TK20 and have been using Duracell NiMH 2650 mAh batteries. Got them in a 4 pack the same time as the light and used the other two in my ZL H501 headlamps. Those don’t seem to be having a problem but in the TK20 they are nearly dead within a week of none use. Noticed I was not getting good runtimes from the start but couldn’t put my finger on the problem until I recharged them and placed these within the TK20 and didn’t use it for 7 days. Couldn’t even run the general mode right. Took the proven Duraloops from my L2D-Q5 and topping them off right now for a test. Guessing this will take a week to rule out the higher capacity standard Duracell’s. Don’t want to test this using alkaline batteries for obvious reasons. Just checking if anyone else ever had a constant fast drain on a TK20. Guess if the batteries are found to be at fault will ask about the performance of the 2650’s in the battery section of CPF. I have used the same type in my GPS in the past and they worked for well.