Battery for Arduino Nano and motor

Hi everybody,

I am currently developing an Arduino datalogger with an Arduino Nano and a micro SD card. It logs data from two load cells. My problem is the following: I would like to make the device portable, so I was wondering which kind of battery would fit best with the following issues:

  • the whole thing needs maximum 250 mAmps to work;
  • it must last at least two hours;
  • the battery must be between 9 and 12V;
  • the size of the battery must be limited (605030 maximum).

I already looked for some batteries but I am not sure of the choice: NiMH seems to be suitable but I fear voltage drop, and LiPo seems too powerful and dangerous according to what I saw.

What do you think would be the most suitable?

Many thanks for your answers,
Alexis