There are basically two types of digital camera batteries. One is the standard AA type and the other is rechargeable. The latter is also known as a proprietary battery as it made by the same manufacturer.
A proprietary type of battery is comparatively more expensive, lighter in weight and more tight and compact. The cost makes the purchase of one or two back-ups slightly prohibitory.
The standard alkaline AA size batteries usually have a very short life – at times even less than an hour, when used in a digital camera. These batteries make good back-ups, especially if you are traveling. A better option would be to use the Nickel Metal Hydride (NiMH) batteries for digital cameras, with a charger. This rechargeable option has a longer life and comes at an affordable price.
The other two types of AA size batteries are : the Lithium batteries, which can not be recharged and the rechargeable Nickel Cadmium (NiCD) batteries. The Lithium digital camera batteries last longer than mere alkaline batteries, as well as have a good performance in cold weather. Yet their price and non-chargeability reduce the appeal in comparison to NiMH batteries. It is important to ensure that your digital camera can load a lithium battery. The advantage of a NiCD battery is that it can retain charge when not in use while the disadvantage is that the battery needs to be fully discharged before you can recharge it. This can be very cumbersome and inconvenient.
If you wish to conserve battery life, it is prudent to make judicious use of the LCD screen of your digital camera, s this element consumes maximum power when in use.
If you going to stay away from a power source for a long time, it is always wise to take at least one set of back up. The standard alkaline AA size battery is good enough for this purpose, in case your usual digital camera battery packs up.