So after some chatting with K.C. Lee (https://hackaday.io/KC) on my last project log, I thought i would give the NiMH batteries a test. I knew that NiMH batteries didnt like being drawn totally flat, so i did some research and found that 0.9v was considered empty, but 0.8v was the safe minimum
I had my multimeter on the cells to keep an eye on the voltage, and the timer just tipped over the 4:15 mark when the cells were reading 1.6v. once the voltage had dropped below 2v, it started dropping pretty quick!!
So NiMH > alkaline, but it needs watching so you dont destroy the cells!!