Modern SLR cameras contain powerful computers and multiple motors.
Even compact digital cameras are voracious power consumers.
This article compares the types of battery chemistry, what they mean to the photographer, and how to get the most from your batteries.
There are specific care requirements for certain batteries (see details below), but here are some general guidelines:
Storage. Don't store batteries at high temperatures.
Why? They can self-discharge a lot faster, which is why that flashlight stored in the hot car all summer has dead batteries.
And some rechargeables can be permanently degraded or destroyed by heat and by over-discharging.
Installing. Don't mix battery types, and don't mix used batteries with new ones.
Why? Multiple batteries work as a unit when they all share the same discharge characteristics (current and voltage curves, internal resistance).
Just like with musicians, weak or mismatched batteries can degrade the performance of the ensemble.
That one sour violin can ruin the symphony, and one bad cell can make you think all the cells are bad.
Recharging (if applicable). Recharge fully each time, preferably right before use.
Why? Most rechargeable batteries lose a significant amount of their energy during the first day of storage.
There is no reason to partially charge batteries unless you're really short on time.
Avoid extreme cold. Most batteries have diminished capacity at low temperatures -- some losing most of their capacity just below freezing.
When using in cold environments, store batteries inside clothing to keep them warm until just before use.
Long term storage of most batteries is best in a refrigerator (not in the freezer, and definitely not in contact with food!).
I recommend sealing the batteries inside a vapor-proof enclosure (Ziplock bag will work) to avoid drying the electrolyte in some types,
and to protect your food and beer from any accidental chemical leaks (e.g., due to unseen battery case damage).
Wearing Out. The service life of a rechargeable battery is normally given in terms of the number of full charge/discharge cycles:
the capacity declines somewhat initially, levels out, then after many cycles the capacity drops suddenly toward zero (won't take a charge).
But even in storage a rechargeable will age -- rather quickly in poor conditions, and in any conditions for LiIon type (details follow) -- and will fail after fewer cycles.
Disposal. Batteries can contain various toxic or hazardous chemicals like lead, cadmium, and lithium.
DO NOT discard them in regular waste for landfill or incineration.
Most communities provide free disposal for batteries.
Bargain Batteries? Some batteries are very expensive, especially rechargeable packs for big cameras and laptops.
You can find bargains for batteries on the Internet (such as eBay).
However, some testing has shown that SOME aftermarket replacement batteries do not perform as well as the brand name batteries... even if the cells originate from the same manufacturer.
Allegedly the battery houses sell off their rejects (under-capacity, failed temperature range, etc.) to discounters, and those may end up in the aftermarket replacement packs.
If buying these, seek a money-back guarantee, and do your own performance assessment (e.g., will they take a good charge) as soon as your receive your batteries.