What is a flashlight? It is a storage container for dead batteries as are all other battery-operated devices. We all know this, after all who hasn’t gone to “the dark side” when chasing down that one 9-v that has failed in a smoke detector in the middle of the night?
The question we want to answer here is are rechargeable batteries a better option? In our opinion they are the only option. NiMH (nickel Metal Hydride) batteries can be recharged upwards of 500-1000 times (http://batterysavers.com/rechargeable-battery-life-questions-and-answers/). This, of course, assumes a “source” of power to recharge them – a vehicle battery, working wall plug or a generator. In our opinion they are the only option as Alkaline, non-rechargeable batteries (https://en.wikipedia.org/wiki/Alkaline_battery) become dead weight quickly, sometimes right out of the package and rechargeable Alkaline batteries do not have the (http://www.greenbatteries.com/battery-myths-vs-battery-facts-1/) storage capacity, efficiency or longevity of the NiMH rechargeable batteries.
Another consideration when buying batteries, or any other “powered or fueled” piece of gear is “diversity”. In this case, less diversity is a good thing (try posting that sentence on Facebook!) You will of course have your cell phone (so the government can track you) so one “unique” battery in 2017 and beyond is a given.
However, having to carry chargers for AA, AAA, C, D and 9-v batteries is not smart. Factoring in the chargers you need along with the rechargeable batteries themselves can become a source of weight and confusion, but, like doing your taxes, you must do it! It is worth the investment in time and brainpower. Resign yourself to the fact that you will, most likely, not be able to get away with just one. Make it simple, do your homework, select your cadre of battery operated devices and then compromise on what you can to make sure you have the fewest number of chargers and rechargeable batteries to carry. Reduced weight and increased efficiency are what every prepper should consider in the selection of every component, especially if you plan involves moving from base, or the situation forces you to change plans and abandon a base.
Another consideration is a portable energy storage system which is a science of its own (and the subject of an upcoming post.) These offer some interesting options that will support your rechargeable battery selection and they can be found reasonably priced.
BTW, when a smoke detector does go full-on PSYCHO replace the batteries in them all because they are like lemmings! R.I.P.