...the lifeblood of your phone
Mobile phones run on batteries. Even when not making a call, they keep listening to the network in case a call comes in. They keep in touch with the network so that it knows where they are, and transmit every so often to do so. It is no surprise that when the battery runs down, the phone stops working!Because phones use their batteries hard, and are designed to be small and light, battery performance is a vital issue.
There are three aspects to a battery's performance:
- Standby time - the time that the battery will keep the phone switched on, but not in a call.
Different phones use varying amounts of power when on standby, and if you move the phone around, it has to keep transmitting to log onto the new base. - Talk time - the time that the battery will power the phone during a call.
Calls in or out use the same power. The amount of power used depends on how near the base transmitter is. The max:min ratio is around 1000:1. - Battery life - how long you can continue to recharge and use the battery before you
have to buy a new one.
To some extent, battery life depends on how bad you are prepared to let it get before you replace the battery. In general, mobile phone batteries are like toothbrushes: most people should replace them sooner than they do.
Although some phones can use non-rechargeable (primary) batteries, the vast majority depend on rechargeable (secondary) batteries, of which there are four main types:
Nickel Cadmium
These are the rechargeable batteries most people are familiar with. They are everywhere, and work well enough, but
they are not very good for mobile phones because of one unfortunate trait: they like to be run down between charges.
If you recharge a NiCd cell without running it down first, it comes to expect recharging at that point, and if you
do it regularly, the battery simply considers that point its "low water" point. See
Battery Conditioning below for a cure for this. In general, you should discharge a NiCd
before every other charge.
NiCd batteries are cheap, and give 500 to 700 charge cycles before they die of old age.
Nickel Metal Hydride
These batteries are similar to NiCd, but they do not suffer the "memory effect" or
"voltage depression" as much as NiCd. In addition, they tend to give more capacity than NiCd
batteries of a similar size or weight. They used to cost more than NiCd, but I don't think that is true any more.
In general, you should discharge a NiMH battery once a fortnight if you charge it every day.
Nickel Metal Hydride batteries give a good power/weight ratio, and last between 300 and 500 charge cycles, at which point their standby time survives, but when you make a call, they fade away fast!
Lithium Ion
These are the latest and most expensive rechargeable batteries. They cost a lot of money at present, partly
because the battery includes electronic charge and discharge control circuitry. They have an excellent
power/weight ratio, and do not need to be discharged at all. In fact the electronics inside them stops them doing so!
Li-Ion batteries cost a lot, can be topped up repeatedly without ill effects, and last for around 1,000 charge cycles. As they age, the capacity falls away gradually, so the point at which they are worn out is hard to define. They should last a few years for most people using them in a mobile phone, particularly if you don't have to waste charge cycles conditioning them.
Lead Acid
This is the sort of battery that is used in cars. They are cheap, and don't have to be discharged before charging: they
like regular topping up. In fact running them down can damage them. They tend to be very heavy for the power they give,
and are not used in handheld mobile phones at all, but "transportable" phones did use them.
...and the rest
There is a lot of development work going on to develop other types of battery, ranging from fuel cells that use
lighter fluid to tiny turbine generators that run on diesel, as well as solar-powered and others that I've not heard
of, I expect. There's a huge and ever-increasing market for smaller, better batteries for all sorts of devices.
Battery Care
As mentioned above, you should discharge NiCd and NiMH from time to time, but that's not all there is to it.
The life you will get out of your battery depends to a huge extent on how you treat it, and some of the advice
you are given is just, plain, wrong.
Charging
The best way to charge your phone's battery is to use the charger supplied with the phone. The charger or the
phone (depending on the make of the phone) will care for the battery far more carefully than some of the third-party
chargers on the market.
This is a typical example - if you don't want the technical bit, skip to the next paragraph:
The charger of a Nokia phone gives 12v DC maximum, current-limited to 700mA. This is supplied to the phone,
which checks the battery capacity (reading a labelling resistor build into the battery) and temperature (using a
temperature sensor built into the battery). If the battery is too hot or cold, it refuses to charge it. As the
battery is charged at a steady 700mA, the phone monitors the voltage, which rises steadily till the battery
is full, then rises more slowly when the battery is full. At this point, the phone switches to trickle-charging,
which involves switching the current on and off in short bursts, which helps prevent formation of whiskers within
the cells (too technical to go into here). All the time, the phone checks the battery temperature, because if
the cell gets hot, that's a sign that it is full and charging should be stopped
When you get a new NiCd battery, it is vital that you give it at least sixteen hours continuous charge before using the battery. NiMH don't depend on this as much, but it is still worth doing, to be on the safe side, and considering the price, I'd also do it for a Li-Ion.
The first few times you use a new battery, it should get a good long recharge, preferably 16 hours each time. The capacity of a NiMH or Li-Ion develops over a few charge cycles, so don't expect miracles at first!
To reduce the power your phone uses (and therefore increase how long a charged battery lasts), turn the lights off, and try to leave the phone in good signal conditions. Moving in and out of coverage will gobble power: see how long a battery lasts on a train journey, and you'll see what I mean! When making a call, extend the antenna, and remain in good signal, possibly near a window.
Where possible, recharge your battery overnight. When you charge a battery, it fills up in a non-linear manner: the battery will be 60% charged within 15 minutes, 90% within an hour or two, but completely charging it will take several hours, despite what the phone display tells you.
Never take your fully-charged battery off charge and then back onto charge a few minutes afterwards, because this can confuse the way the phone monitors the battery's charge state. This is a particular problem for car kit users, so take care!
Battery Conditioning
To prevent a NiCd or NiMH battery losing capacity, or to restore one that has suffered this, you can "condition"
the battery. This involves running down all the cells that make up the battery. A cell is an individual element of the
battery, and several are wired in series to form each battery. This is the problem: you have to just empty every cell,
without overdoing it and reverse-charging any of the cells.
Conditioning a battery can prevent the capacity of the battery from falling, but it uses up one of the battery's recharge cycle "lives", so don't overdo it!
Conditioners run the battery down by taking a current out whilst carefully monitoring the voltage that the battery gives. When the voltage drops to 1.0 volts per cell, the discharge stops. If you try to save money by using a bulb and a wire, you will almost certainly destroy the battery. Email me for the gory details of how and why!
cellular. v1.02 10 May 98