9-Cell/80-WHr -- 6-Cell/48-WHr Laptop batteries...what's the difference?

[freedon]

Don't know if they are a standard, but you can choose either of them for a spare battery for the Dell Latitude 800/810. Dell doesn't have a "help me choose" button.


ADD: just figured it out.

Whr = work hour

why would the 48 WHr cost $20 more

[mikeki]

I would bet WHr stands for Watt Hour. A watt is a unit of power, like a 100 watt light bulb. If your computer uses 10 watts then the 48 Whr will last 4.8 hours. The 80Hr will last 8 hours.

Besides capacity, the 9 cell will be a larger size and stick out the back and/or bottom of your computer a little bit and be heavier. If that matters then it's a consideration.

For me? I usually get the big one as the second battery.

[freedon]

Watts but of course! That makes much more sense! thanks

[kent1146]

Mike Ki is right.

WHr = Watt*Hour

The 90WHr battery has about twice the battery life of a 48WHr. If you're going to be using battery power on your laptop for more than 2 hours, go with the 90WHr battery. Nothing sucks more than having your laptop battery die when you're watching a DVD on a plane.

[slavik]

aren't batteries rated by Amp*hour???

watt*hour = joule ...

[kent1146]

You are right that Watt*hours can be converted to joules. 1 Watt*second = 1 Joule. It is a measure of energy defined by Power * Time.

If you look on your electrical bill, you will find a measure of KWHr, or kilowatt*hours. It is a measure of energy, and can be converted to the SI unit joules.

Batteries, similarly, have a measure of their energy capacity defined in a metric of Power * Time. A 90WHr battery can deliver 90 watts for 1 hour, 45 watts for 2 hours, 30 watts for 3 hours, etc. Power * Time = Energy.

Now, Power = Voltage * Current. Plug this into the equation for energy, and you have:

(Voltage * Current) * Time = Energy.

Watt*Hour and Amp*Hour can be converted between each other, ONLY IF VOLTAGE IS A CONSTANT (this is why you will see amp*hour ratings accompanied by a voltage). Since a LiIon battery manufacturer has no idea what voltage the battery cell will end up powering, they will go with the more universal rating of W*Hr.

[slavik]

Ahh ... I see, thanks.

And I don't pay electric here ;)

Also, Aren't Laptop batteries usually something like 10.8V???

Originally posted by kent1146
You are right that Watt*hours can be converted to joules. 1 Watt*second = 1 Joule. It is a measure of energy defined by Power * Time.

If you look on your electrical bill, you will find a measure of KWHr, or kilowatt*hours. It is a measure of energy, and can be converted to the SI unit joules.

Batteries, similarly, have a measure of their energy capacity defined in a metric of Power * Time. A 90WHr battery can deliver 90 watts for 1 hour, 45 watts for 2 hours, 30 watts for 3 hours, etc. Power * Time = Energy.

Now, Power = Voltage * Current. Plug this into the equation for energy, and you have:

(Voltage * Current) * Time = Energy.

Watt*Hour and Amp*Hour can be converted between each other, ONLY IF VOLTAGE IS A CONSTANT (this is why you will see amp*hour ratings accompanied by a voltage). Since a LiIon battery manufacturer has no idea what voltage the battery cell will end up powering, they will go with the more universal rating of W*Hr.

[kent1146]

Laptop battery voltage will differ, depending on the laptop.

This is why their batteries are rated as WHr, and not AHrs.

[mikeki]

Mike Ki is right.
Why can't I ever get my wife or teenage kids to say that?