Mobile phone batteries

Article ID : 34
Created on 2007-07-13 at 3:34 PM
Author : Rahul Bhanot [rahulbhanot@yahoo.com]

The battery is the lifeblood of your mobile phone. With a flat battery, it is of little use, and one of the biggest frustrations of mobile phone use is battery life.

Designers of mobile phones try hard to minimise the power they use, which gives longer service from smaller, lighter batteries, but although the power used on standby drops through clever design, the power needed for the transmitter does not. This means that a phone with a week or more of standby time may still only manage an hour or two of calls before its battery is flat.

Some handsets can take primary (non-rechargable) batteries. This can be useful in an emergency, but if you do it regularly, the battery costs will be huge! Some handsets nearly manage to take "ordinary"batteries. For example, the Motorola c520 works with 4 AA batteries, but the standard battery cover won't fit back on: at a pinch, use an elastic band!

Rechargeable battery types
There are three basic types of rechargeable battery used in mobile phones.

Nickel Cadmium (NiCd)
This is the rechargeable battery that most people are familiar with. This technology has been around for many years, and rechargeable NiCd batteries are commonplace. They have two major drawbacks, which mean that most quality mobile phones no longer use NiCd batteries:

Heavy metal The chemicals in Nickel Cadmium are not environmentally friendly, and the disposal of cadmium-rich waste is an increasing problem.

Memory effect This is sometimes referred to as voltage depression. If you do not fully discharge a NiCd cell before recharging it, after a few cycles, the battery "learns" this low water mark, and acts as if it is discharged at this point.

The work-around is simple: you have to run the cell down before recharging it. Unfortunately, it is not always convenient to do this. You want the phone to be available for use, not sitting running the battery down. In addition, the cells are connected in series, so although some cells may be discharged, others may not be.

There are specialist battery conditioners which claim to cure this problem. Some of them even work to some extent!

Nickel Metal Hydride (NiMH)
Nickel Metal Hydride batteries claim to be superior to NiCd not only because they don't contain cadmium. They also are less prone to the "memory effect" problem, and a discharge every week or two is ample, unlike NiCd which need to be run down every other charge to retain their capacity. They also have a higher capacity in relation to their size and weight

The drawback of NiMH is that they don't seem to last as long as NiCd cells. After a few hundred charge cycles, the crystals inside NiMH cells become coarser, and although they are able to provide the power for long standby times, when the extra current to sustain a call is needed, the voltage available drops rapidly, and suddenly you're getting Low Battery warnings. End the call, and after a few minutes rest, the battery is fine for many hours standby. That's OK unless you want to use your phone!

Lithium Ion (Li-Ion)
This is the current "latest and greatest" technology for mobile phone batteries. Li-Ion gives exceptional capacity for its size and weight, and does not suffer from the memory effect. This means that you can top up the charge whenever it is convenient. The only real drawback of Li-on is that they are expensive, and so they tend to be supplied only in top-of-the-range phones. You should avoid completely discharging Li-Ion batteries

There are also Lithium Polymer batteries, but these are very similar to Lithium Ion, except that they can be moulded into more varied shapes, and so be squeezed into smaller phone casings.

Looking after your battery
Click Here For information about how to care for your mobile phone's battery.