FWIW, you'll need to experiment with NiMH AA or AAA rechargeables in your devices. Some do very well with the slightly lower voltage in NiMH, while other devices need the full 1.5v per cell to operate as expected.

I started using NiMH about 20 years ago after switching primarily to digital for my "serious" photography with my first Nikon dSLR and SB-800 flash and peripherals. The SB-800 performed perfectly with NiMH rechargeables, as did my compact P&S digital cameras.

But other devices with constant drain -- pre-LED flashlights, portable radios -- tended to poop out quickly with NiMH AA and AAA batteries. It's possible that newer constant drain devices like flashlights and radios may be efficient with NiMH batteries. All of my shortwave portable radios are from the 1970s-90s, but some of the newer generation DSP shortwaves may run just fine with NiMH rechargeables.

I've also tried lithium AA and AAA batteries in bicycle lights for winter use, but the expensive lithium cells didn't last long, although they did seem to work well in cold weather. But we don't get enough seriously cold weather to make it worth the expense.