As you may have heard here previously, I own Redsun's "other radio", the RF-1210. This is an analog-tuned, multi-band portable radio with a speaker approximately 3 inches in diameter. It looks a lot like the Tecsun R-9700DX. I've been using it primiarly for mediumwave in my kitchen and dining room during the morning. This means that it is used for 30 minutes at most per day.
It is powered by four AA batteries, and I have been feeding it with Energizer 2500 mAh NiMH batteries. They're charged in an Energizer battery charger, which states on the back that it can charge AA batteries up to 2500 mAh.
It seems to me that the past two times the batteries ran out in this radio, it was only after about a month of use. The way I'm informed of the battery drain is that the audio quickly reduces in volume. I turn the knob to increase the volume, then it fades rapidly again, becoming inaudible.
I haven't beeen measuring the voltage level of the batteries before insertion, which I should try next time. Using my multimeter, here are the battery voltages after removal:
I wish rechargeable batteries had serial numbers so I had an easier way to track individual battery behavior. The 0.14-volt battery is a concern; it should be charged right away. For now, I decorated the slacker battery with masking tape that has "0.14" written on it.