Cordless phones are so loaded with features these days, that when you are shopping around it's easy to lose track of what's truly important. Conveniences such as telephone books, Caller ID, and pager notification make you forget that if your handset can't hold a charge, you might as well use a corded phone.

So which rechargeable battery is best? Nickel-cadmium (Ni-Cd), nickel-metal hydride (Ni-MH), or lithium-ion (Li-Ion)? Which has the longest life? After reading this, you might be able to distinguish between each technology and know which best meets your needs.

Ni-Cd batteries were one of the first ones used in cordless phones. They were (and still are) known for quick charging rates and even better discharging rates, making them ideal for sporadically used products that require lots of energy (such as power drills). Unfortunately, they do not have high capacities and they do contain Cadmium—a toxic metal that is quite heavy—so they are not particularly well suited for cordless phones.

Another drawback of Ni-Cd batteries is that they are subject to "memory effect." This phenomenon occurs when you repeatedly recharge batteries before they are completely depleted. Doing so reduces the talk time of the phone, often permanently altering a battery to 50% of its original capacity. Memory effect can be avoided by allowing your battery to completely discharge before recharging.

Nickel-metal hydride (Ni-MH)

Often interchangeable with Ni-Cd batteries, Ni-MH batteries provide 20% to 30% more capacity, are lighter in weight, and do not contain heavy, toxic metals. Ni-MH batteries are also much less susceptible to memory effect, but completely draining them every 8 to 10 uses is advisable.

Lithium-ion (Li-Ion)

Li-Ion batteries are the best all-around rechargeable batteries on the market today and, as you would expect, they're also the most expensive. They have 50% more capacity than NiCd batteries and are much lighter in weight than either NiCd or NiMH, making them ideal for laptop computers and cell phones. They are not susceptible to memory effect and do not pose a significant environmental problem for landfills.

One of the best attributes of Li-Ion batteries is the way they deliver power. While Ni-Cd and Ni-MH batteries lose overall strength as they are used, Li-Ion batteries hold and deliver full power during most of their use cycle (and then quickly deplete to zero charge). This facilitates reliable cordless performance throughout a battery's use. The cost of these batteries prevents them from being used in most low- to middle-end cordless phones.

Tips to get best of your battery

If you're unhappy with the battery capacity of your present cordless phone but don't feel like upgrading, here are a few things you can do to improve your battery's performance:

After your initial cordless phone purchase, make sure you give your handset a full, uninterrupted charge. Often this will take as long as 12 hours.

Regularly clean the contacts of your battery with a cotton swab and alcohol to prevent corrosion.

If you have a Ni-Cd battery, drain it regularly until it can no longer function. Beware, though, because completely discharging the battery every time you use it can also diminish capacity. It's best to "cycle" the phone every 3 to 5 times you use it.

If you believe your battery is suffering from memory effect, you can have it reconditioned by a battery analyzer. These machines typically cost a few hundred dollars or you can pay a one-time reconditioning fee at an electronics store.

Dispose of your present battery and get a replacement from the manufacturer,  or a battery dealer.

When you recharge a Ni-Cd battery before it is completely drained, bubbles form on the battery's plates thereby significantly reducing the surface area needed to produce electricity. This process is commonly termed "memory effect," but is often incorrectly applied to problems that should be attributed to "voltage depression." Voltage depression is caused by, overcharging. It can be remedied by depleting the battery completely and then recharging it while making sure it does not overcharge, i.e., don't leave the handset in the cradle for more than 12 hours.

Coke trick:Once a year, you should take regular Coke (the drink, not the drug!!) and clean the connection points on your cordless phone and your base. Coke can be used to clean corrosion off of your phone and base. Excess corrosion on the connection points between your cordless phone and the base will but a straight on your battery.
The instructions for this measure should be followed exactly or you may risk doing damage to your phone.
You will need a can of regular Coke (not caffeine free or diet), a glass, an area to let it sit, and a small cloth.

And if you are planning to replace your old battery with a new one:

Make sure that you pay attention to the voltage and amperage of your old battery. If you have changed the battery in the past, make sure that you are using the correct voltage and amperage for your current battery. This can be found in your owner's manual.

The voltage of the cordless phone battery is the amount of energy that the battery needs to charge. It is usually the first power number that is listed on the cordless phone battery, and will almost always be a number between 6V and 12V.

The amperage is the amount of power that the battery will pull off of the electricity while charging. This will usually be the second number on the cordless phone battery and will range between 300mah and 900mah.

These numbers should never be strayed from. To keep it simple, your battery could wear out a lot faster, or ruin the phone, if the numbers are wrong. In extreme cases (i.e. if you are way off on the amperage) you could cause the cordless phone to catch fire while it is charging. (always consult your user's manual which comes with your phone before changing the battery)