@ahmedadelhosni
Alkaline, cheap "IKEA" batteries..
My units reports around 60% battery capacity left (very unscientifically measurements)
About operating frequency. If you have a sleeping node, then you won't gain anything from using 1Mhz versus 8Mhz, on the contrary you might end up using more power, when using 1Mhz, than 8Mhz. Because the time that the MCU is awake is longer at 1Mhz, than at 8Mhz. Remember, that when the MCU is sleeping, the power usage is the same, regardless of what frequency the MCU is working at, because the oscillator is shut down.
at 8Mhz you would complete your operation quicker, and return to sleep mode again faster, than when running at 1Mhz.