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My 4 year old Dell Inspiron battery is very poor and I have been thinking about a replacement. I have also been thinking about getting a new up-to-date laptop with windows XP.
Rather than getting a Dell replacement I thought I could get an external battery which could be used on future laptops and possibly low power 12v TVs. I've been looking Here but does anyone know how to interpret the watts/hours figures quoted Some say 6.8 watts/hour and another over 133 watts/hour. So for an average modern laptop surfing, how many hours should one get out of 133 watt/hours
1) I suspect the 6.8 is a typo with the decinal point in the wrong place, and should be 68.
2) Watt/Hours doesn't make sense - it's sort of accelerating energy, which hopefully doesn't sound sense to you either. Watt-Hours it should be.
3) How long is a piece of string, because it depends on what processor you have (how efficient it is), what power settings you have (eg screen brightness, hard disc rundown, etc), etc.
But to stab in the dark, say a couple of hours intensive use from a reasonable battery? Work out the watt-hours per £ ranking and see how this matches the watt-hours ranking?
I have found this all very confusing. When looking at laptops in a shop the assistants don't seem to be able to give any specific details of power consumption. I have deduced that the number of hours they say they last is the best comparison. The cheepest ones say 2 hrs and the more expensive up to 5hrs. Now with these external batteries they seem a lot larger than the built in ones so if twice as big one might expect twice the capacity.
Remember if you use any extras such as external dvd writer, external hard drive, tv card or similar, these take power from the battery thus reducing time between charges.
Unless you are using the laptop where no external power source is available battery life is upto a point academic, an inverter is a good investment for using in the van or your car.
If you want to know how much energy an external laptop battery contains compared with the internal - here goes.The energy in the battery is measured in WattHours (i.e. watts multiplied by hours). The writing on the website W/hr is a common mis-typing. As an example a litre of petrol will contain about 8889Watt hours of energy which can be released by burning it. 8889Whr of energy is often written as 8.89kWhr. This is a bit less than the amount of electrical energy used in your house in a day. Now U know why we mostly have petrol in our tanks rather than batteries.
Imagine you have a laptop with a 15volt battery. As lanerider uk says..
"Watts = volts x amps" which is a measure of power (not energy). We can work out the energy from the following:
Watt Hours = volts x amps x hours.
So my Dell laptop battery is marked 15 volts and confusingly 4460mAhr which is the same as 4.46 Amps x hours. So my laptop battery volts x amps x hours is 15 x 4.46 = 67 watt hours. An external battery of 67 watt hours would only be as good as my internal one if there were no losses involved in getting the energy out of the new external battery and into the laptop. (In practice the efficiency of this will probably be only about 80% so I would want an external battery of about 84Whrs). The output voltage of the external battery has to match the input voltage that the laptop uses, so u need to check their compatibility tables carefully. Hope this helps. regards W.
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Some say 6.8 watts/hour and another over 133 watts/hour. So for an average modern laptop surfing, how many hours should one get out of 133 watt/hours 
