Understanding 10mAhr and 10Whr Ratings for Laptop Batteries

[jackson6612]

10mAhr stands for a current of 10mA for one hour.

10Whr stands for power of 10W for one hour? i have seen this kind of rating written on a laptop battery. Please confirm if have it right. Thanks.

Please remember I am not a physics or science student.

 

[jtbell]

10mAhr stands for a current of 10mA for one hour.

Possibly. It could also stand for a current of 5 mA for 2 hr, or 20 mA for 0.5 hr, etc. It's a measure of the total electric charge that the source can deliver.

10Whr stands for power of 10W for one hour?

Possibly. It could also stand for a power of 5 W for 2 hr, or 20 W for 0.5 hr, etc. It's a measure of the total electrical energy that the source can deliver.

 

[jackson6612]

Thanks a lot, JT.

My friend has a netbook Dell Mini and I think it consumes around 60 watts and has a 56Whr battery. It could run for hours on a single charge. 56Whr would mean 56 watts for one hour and the mini taken in about 60 watts, then how come it could run for hours? Could you please help me?

 

[Vagn]

Thanks a lot, JT.

My friend has a netbook Dell Mini and I think it consumes around 60 watts and has a 56Whr battery. It could run for hours on a single charge. 56Whr would mean 56 watts for one hour and the mini taken in about 60 watts, then how come it could run for hours? Could you please help me?

Are you sure it is a watt-hour? Not kilowatt-hours, which tend to be a more common unit. For example electricity is often charged as a certain amount per kilowatt-hour.

 

[JaredJames]

My laptop battery is rated at 47Wh, 4200mAh, 10.8V. (I checked for this thread.)

 

[Borek]

Are you sure it is a watt-hour? Not kilowatt-hours, which tend to be a more common unit.

kWhr for a laptop battery? Assuming energy density around 200 Wh/kg (that's a little bit more than my laptop's Li-ion has) you will need 5 kg battery for that. Technically possible, but hardly portable.

My laptop works around 10 hours in energy saving mode, but only about 2 when pressed hard.

 

[JaredJames]

Based on my above figures: 47Wh, 4200mAh, 10.8V.

That means the most (safely) my battery could deliver in power is 4.2A x 10.8V = ~46W.

So if it ran at full power, drawing the maximum the laptop can, the battery would only last for an hour.

An example of this would be for you to use processor intensive software, watch a HD video, all whilst burning a CD. It will reduce battery life right down, possibly below the hour figure.

However, if you only browse the internet and view a few files, you won't draw anywhere near the maximum amount and the battery will last significantly longer. In my case, upwards of 3 hours. So this tells me that under light use it is only using 1/3 of overall power available to it.

What the battery can deliver, and what the laptop is drawing are two different entities.

 

[sophiecentaur]

It may not be a good idea to max-drain a battery (not your own one anyway) so don't go connecting big fat load resistors to it just to prove a point. ;-)
I think your original 60W figure will refer to approx maximum power used - disc flying, screen bright and brain working flat out. They do try quite hard not to work that hard, I imagine so that will be why you get much longer than 1Hour out of your battery.

 

[JaredJames]

NEVER fully drain a Li-Ion battery. It will damage it.

 

[Redbelly98]

Thanks a lot, JT.

My friend has a netbook Dell Mini and I think it consumes around 60 watts and has a 56Whr battery. It could run for hours on a single charge. 56Whr would mean 56 watts for one hour and the mini taken in about 60 watts, then how come it could run for hours? Could you please help me?

My best guess is that the 60 W figure is a maximum power consumption, but in practice it uses much less power.

My Dell Latitude laptop normally uses about 20-25 W of power, something I measured several months ago using an electrical power meter. But printed on the laptop it says "Input: 19.5 V, 4.62A", which would correspond to 90W. One wants a power supply capable of handling the maximum power required, but the actual, average power consumption can be considerably less than that.

 

[cjl]

Thanks a lot, JT.

My friend has a netbook Dell Mini and I think it consumes around 60 watts and has a 56Whr battery. It could run for hours on a single charge. 56Whr would mean 56 watts for one hour and the mini taken in about 60 watts, then how come it could run for hours? Could you please help me?

I would be very surprised if it consumed 60 watts most of the time. Most notebooks run in the 9-30 watt range at idle, with small and power saving computers (like a Dell Mini netbook) being more towards the lower end of that range (9-12 watts). So, I'd expect it to run 4-6 hours on a charge. 60 watts might be the size of the power adapter, but the computer itself requires far less most of the time. For example, I've measured my Alienware M11x at 12-22 watts at idle, depending on what power mode it is in, and I would guess that it pulls more power than most netbooks.