After you have considered all the pros and cons about whether you should buy a laptop or not, here's another spanner in the works.

A laptop would not be so portable if it did not have some kind of portable power supply that it can use while on the road. Enter the little (sometimes not-so-little) battery pack.

Technology in the laptop world has been improving ever since they were introduced on the market; laptop batteries have been following suit.

On the market today are three main battery types.

The first laptop models featured the nickel cadium rechargeable laptop batteries. They were cheap to manufacture and their output was quite high, compared to the cost of making them. Their popularity diminished, mainly due to their weight. Their efficiency was inferior to that of newer batteries.

Although used for older models, Nickel Metal Hydride (NiMH) batteries are still quite popular. This type of rechargeable battery was a big step in the notebook world, partly because they were more reliable and had a higher output than NiCd batteries. This type of battery was also cheaper to produce and safer for end users. The main drawback was that they were prone to "memory effect". If the battery was not drained of its full load of power and plugged to a charger or the laptop plugged to the mains supply, the battery would "remember" the power level it had prior to plugging.

People have tried unbelievable methods to have them reset this memory effect, such as wrapping batteries in plastic and sticking them in the freezer for two hours. Some people say that you can deep-cycle (discharge and recharge) these batteries and you actually gain some more life out of them. Normally, you should only deep-cycle a battery every 30-40 charges to re-calibrate the battery meters in the electronic device.

The best strategy is to buy a new one and take care of it properly. Hopefully it will last longer. Care involves letting your battery drain until your laptop goes into sleep mode due to lack of battery power. Then, and only then, should you plug your laptop into the mains supply. This might be a bit hard to do especially if you happen to use your laptop on the road all the time.

You can have a good look at your laptop's manual because there are some laptops on the market that actually have a feature of performing a deep cycle on the battery for you. Ask about it when you buy your laptop with a NiMH battery.

Lithium ion (Li-ION) batteries are used in most laptops today. They do not suffer from the memory effect like the NiMH batteries and are lighter than NiCd and NiMH batteries.

The downside is that they are the most expensive power sources for laptops.

A rule of thumb that may be helpful is that if your laptop works fine on mains power while its battery is unplugged, then proceed accordingly. Batteries are more affected by heat than anything else. The heat produced by a laptop is designed to keep it away from the battery, but if you don't need the battery in, you're better off taking it out and storing it somewhere away from the heat produced by the laptop. Preferably in your fridge. Really!

Another thing to consider is whether to get a bigger battery with your laptop, and by bigger I mean in relation to the number of cells. Batteries come in a four-cell, six-cell, nine-cell or a 12-cell configuration. Main decision here: working duration of laptop vs. heavier load to carry on your shoulders! Naturally, there is also the financial dilemma between these.

Batteries are measured in voltage (V) and milliamp-hours (mAh). Voltage represents the drawing rate of energy from the battery. There are cells inside a laptop battery and each of those is typically 1.5 volts. These cells are connected to form a battery. Milliamp-hours represents the capacity (or run time) of the battery. The higher the mAh rating, the longer the run time. Longevity is dependent on usage. Another option to consider is to buy a similar spare battery and carry it around with you or to buy a battery with more cells, which is better performance-wise.

To conserve power on a laptop you might want to check that your OS settings are configured correctly for a laptop i.e. hard disk spin-down, screen blanking etc. Remember that LCD panels (display screens) typically account for about 30 per cent of overall notebook power consumption. The hard drive on average consumes about eight percent of a notebook's overall power.

Bottom line: if you have the choice and the cash, buy a Lithium Ion power pack but if you don't, the next best thing is the NiMH, and with a bit of effort on your part this type of battery will serve you well.

All these power packs are recyclable. If carelessly discarded, they can damage the environment, so do not dispose of them in your rubbish bin. Locate appropriate containers where dead batteries are collected and recycled and do the right thing.

If you require more detail about batteries visit http://batteryuniv ersity.com/.

Mr Marshall, a certified computer programmer and technician, is giving regular tips in i-Tech on the best and safest use of computers. He can be contacted at noelmarshall.itech@gmail.com.