NI-MH batteries are popular with photographers for use in photographic flash equipment. The batteries are readily available at virtually any store in the western world and work well with camera equipment. They provide excellent rush current compared to traditional alkaline batteries and both of those are much better than old heavy-duty or carbon batteries.  Neither alkaline nor carbon batteries were designed for high-demand current devices like modern photographic flashes and digital cameras. Ni-MH batteries are rechargeable and can be used almost for unlimited number of times. However, alkaline batteries are primary cells and the moment they are exhausted, they must be thrown away.

For all the advantages of Ni-MH batteries, there are several disadvantages. The first is that they have a much higher self-discharge rate than any other type of battery. This may not seem significant until one tries to use batteries charged last month, only to discover that the NI-CD rechargeable batteries have discharged to the degree that they cannot be unusable. It is very important to make sure the batteries are charged fairly regularly and certainly the evening or day before they are to be relied upon. Photographer often let the stockpile of batteries go for a while and tried to use them in a rush only to discover that regular maintenance and upkeep is necessary with Ni-MH batteries. Some manufacturers suggest not allowing the cells to dip below 1.0V, otherwise permanent damage might occur. Always stay on top of your Ni-MH. There are some hybrid batteries out there which can avoid this issue.

Secondary issues with Ni-MH batteries are the primary cell voltage, resistance to cold and hot temperatures, recharge time and required recharge technology.

The impetus of the lab testing and measurement series of 18650 batteries was several of the batteries refused to power up some flashes on a regular basis. It was unknown if the batteries had just been sitting around that long or if there was something else going on. But NI-MH batteries will always give you confidence in their ability to power devices for a long time.