Are Primary and Rechargeable Batteries interchangeable amongst each other?

Not all battery types are interchangeable. However, in the consumer, household small format battery category, the following types of the same format can in most cases be interchanged: Heavy Duty, Alkaline, Rechargeable Alkaline and NiMH batteries. Although primary and rechargeable alkaline batteries are rated at a nominal voltage of 1.5 volts, as they begin discharging, their voltage continuously drops. Over the course of discharge, the average voltage of alkaline batteries is in fact about 1.2 volts, very close to NiMH batteries. The main difference is that alkaline batteries start at 1.5 volts and gradually drop to less than 1.0 volt, while NiMH batteries stay at about 1.2 volts for most of the service time. However, NiMH batteries make only practical sense in very high drain devices such as digital cameras as their self-discharge rate is too high for applications that require power of long periods of time. For those slow discharges, a battery type with a very low self-discharge rate is required. Rechargeable Alkaline will fit the bill there. Remember, whatever battery type you use, NEVER mix battery types for use at the same time and never mix old and new batteries. Keep batteries in sets for best performance.

How should batteries be stored?

Remember, batteries are like any other chemical system. Heat will accelerate the chemical reaction and shorten cell life. Therefore, the greatest threat to a battery's useful life and shelf life is heat. So, avoid storing batteries or battery-operated devices in extremely warm places; store them in a cool, dry place.