There are probably items in your survival kit which require power. There is a very good chance that in a survival situation, there will not be a (working) wall outlet available. So how do you power these items?
The first and most obvious option is batteries. Each device should have fresh batteries in it, protected from accidental activation. One way to do this is to put a piece of cardboard or plastic between batteries or in front of one of the contacts. Be aware of how long a set of batteries will last in each device, and where needed and practical, include spare set(s) of batteries. Make sure that any spare batteries are packed in such a manner that there is no chance of them shorting out.
There are really only two choices of battery type to consider, Alkaline and Lithium. In most cases, Lithium are a better choice, since not only do they tend to provide for a longer run time, but they can have a longer shelf life as well. Besides, they work better in temperature extremes. They are pricier and harder to find though, so Alkaline can be an adequate alternative.
If your device(s) will work with them (since rechargeable batteries generally put out 1.2 volts per cell as opposed to the standard battery cell voltage of 1.5 volts), rechargeable batteries can be an option as well, if and only if you have a way to recharge them. Recharge possibilities include a generator (crank), solar panel, or a larger external battery pack. Why is a recharge capability “mandatory”? Because rechargeable batteries have a tendency to “self discharge” while in storage. Make sure that your charging equipment is appropriate for the battery technology you choose, as the charge rate curve varies between the different technologies. Note that in some cases, the “recharge” methodology might be able to run the device directly, although this is not as effective as a “power storage” methodology to provide power when the sun is down or you get tired of cranking.
Every charge/discharge cycle slightly diminishes the battery capability. Generally, a good quality rechargeable will tolerate hundreds of cycles before the capability is significantly reduced, so this may not be a critical factor in survival usage.
There are a number of battery technologies to choose from. The earliest one, Nickle Cadmium (NiCad) is a poor choice, not being particularly effective, and worse, self discharging very quickly. Nickle Metal Hydride (NiMH) is a better choice, but still not optimal. Lithium Ion (Li-Ion) is the current top choice, with the best performance and least amount of self-discharge. There are a number of experimental technologies being worked on, but that does not help us now.
Lead-acid (“wet”, like in your car) batteries are very good, but tend to be too heavy due to the lead and too dangerous due to the acid for most survival kit usage. An interesting option appeared on the scene several years ago, but seems to have petered out. This was “rechargeable alkaline”. The advantage of this was that the voltage was 1.5v, and it was claimed not to self-discharge. The downside, and perhaps the reason for its demise, was a very quick disintegration of capability, becoming marginally useful after only ten or fifteen charge/recharge cycles. Even if you can find some of these, they may not be a good choice, as the charging equipment was different significantly different from the other technologies and might not work with common survival recharge methodologies.
Rechargeable batteries have a rating of “maH”, which stands for “milli-amp hours”. This is an indication of “how much” power the battery will hold. Let us say you have a battery rated at 1000 maH. Theoretically, it could put out 100 ma for 10 hours. Don’t count on this though, particularly at the low end or high end of the current draw. It is only a guide to the relative capability between two different batteries. Make sure you run each battery through a couple of charge/discharge cycles before putting them into your kit; I’ve found some batteries rated very high which turned out to be far inferior to lower rated batteries, and others which self-destructed on the first use. Name brand batteries seem to be a “safer” choice over highly rated “no-name” batteries, but even then the name is no substitute for actually testing them prior to “trusting your life” to them.
I like the “Waka Waka” power source as a compact, reasonably priced solar panel/storage battery/light source/emergency signal option. The problem is the power button is very easily accidentally pressed, draining the battery. Every single time I’ve tried to carry one or pack one, I found it discharged later. One of these days, I’ll have to create a button protector for it.