I have been using a single grand exclusively for about 6 months now (this is my only mod). When I first started using it, I would get an entire day from one battery. Now, using those same batteries, I am going through 3 batteries per day. (They are AW IMR 2000 batteries.) My juice usage has actually decreased in that same 6 months. When I first started, I was using a bottle per day. Now I am using between 1/2 to 3/4 of a bottle per day. I pull my batteries (usually) between 3.6 and 3.7 volts. The lowest (in my memory) that I have let the battery go is about 3.5 volts. I have three batteries in rotation, so they get to rest about a day between being charged and used. I always check them before inserting them in the REO, and they are 4.21 (one is 4.20). Is this an indication that these batteries are failing? Should I just replace them (and thank them for their valiant service)? I am using a RM2, 28 awg with 8/9 wraps on a 5/64 mandrel (about 1.2 - 1.3 ohm) and XC-132 wick.