A great example of this is my PowerTap P1 pedals for the bike or the Brother P-Touch label makers. Lithium-ion is much more expensive and is best for the opposite case, where you need constant voltages and lightweight such sensitive electronics. It is the default choice since they are cheaper and will run longer (at lower voltages) than Li-ion batteries. TL dr, the main point is to get the Fujitsu HR3UTC if you have things that don't need constant voltage, so for instance flashlights great, it will be slightly dimmer (1.5V for Lion vs 1.4V going down to 1.2V for NiMH). TL dr Get Fujitsu HR3UTC NiMH for long life and low cost, Pownergy Li-ion for high voltage or light weight They have less capacity than NiMH but they produce their 1.5V uniformly before failing, so this is nice for applications that can't deal with gradual voltage loss.They are pretty hard to find and expensive because everyone (cough, the EV, phone and laptop industries need them).They do need new chargers which are tuned for this new battery chemistry and some just have a microUSB sticking out so you don't need to buy a LiPo battery charger.They are all internally really running at 3.4V, so they need step down electronics to get to 1.5V.Not that it matters in these applications, but they are definitely lighter, so if you have something that is weight critical like say a set of Garmin Powertap bike pedals, then this is a big deal.However, the big move now as with all things is to Lithium-Ion, this has some advantages and then some disadvantages: They have gotten quite cheap at less than a $1 per cell, so never as cheap as alkaline batteries, but they last over 500 charges, so you are saving a lot.For instance, our Brother P-touch is a label maker that really wants to see 1.5V They generate 1.4V, so slightly lower than the 1.5V so some things won't work with them as they need that much voltage.If you don't get the Eneloop or other low discharge batteries, they will run down in a month or so.
We have the LaCrosse chargers and there are really two limitations to them: They are a great way to save the environment and they are cheaper too. Well, I've been using various NiMH batteries in the AA (aka LF-91) and AAA (aka LF-92) form factors for over a decade now.