# HP tc4400 Tablet PC: exceptional battery life or funny math?

Warner Crocker points out some interesting power consumption stats that HP has stated for their new tc4400 Tablet PC. According to HP, the tc4400’s primary battery will keep you running for 5 hours and 30 minutes. Also available are two optional batteries: an 8-cell Extended Life battery and a 12-cell Ultra-Capacity battery. It appears that you can pair either of these optional batteries with the primary, providing run times of 12.5 or 16 hours, depending on using the 8- or 12-cell battery.

Now, I’m no expert on power consumption, but I was pretty good at math back in the day. Considering we’ve got several folks researching battery consumption for the first gen UMPCs, I’m hoping someone can check my math to see if I’m off base with the following conclusion.

Let’s start with some facts directly from the HP official spec sheet on the tc4400:

• Primary battery capacity = 55 Wh
• Extended battery capacity = 52 Wh
• Ultra-Capacity battery capacity = 95 Wh
• Average Operating Power = 21 W

Again, I’m not an expert on power consumption, so I’m asking those who are to validate my theory and my math. The way I understand it, we can divide the battery capacity (in Wh) by the operating power consumption (in W) to determine the average or "real world" expected run-time. If that’s correct, let’s do the calcs for each battery configuration:

• Running on the Primary battery alone = 2.6 hours or 55/21. HP states "up to 5 hours and 30 minutes"
• Running on the Primary and Extended battery = 5 hours or 107/21. HP states "up to 12.5 hours"
• Running on the Primary and Ultra-Capacity battery = 7 hours or 147/21. HP states "up to 16 hours"

I’m sure that with your power management set to be as judicious with juice as possible, you’ll likely get some good run time on the tc4400, but I have to question the stated run times. I also realize that most computer manufacturers express the "best scenarios", but do these numbers on the spec sheet sound high or is it just my lack of understanding on how run times are calculated?

-kct

Agnes

I have tc4400 too, and I get approximately 2,5-3 hours at normal usage. However the software checking the battery is somewhat funny, because it says 1hour 55min battery runtime, but I can make notes for almost 3 hours continuously using Xournal with bluetooth off and screen brightness at maximum.

sweetaj

I have a tc4400, 2.0ghz core2, 3gb ram, etc. Normal use for me at the lowest screen settings is about 2.5-3 hours with the battery only being a few months old. Even out of the box with wifi off and brightness down I only got 3.5 if i was lucky. If you need to use it all day without plugging in it looks like you’ll need 2 extended batteries to add to the standard.

sweetaj

I have a tc4400, 2.0ghz core2, 3gb ram, etc. Normal use for me at the lowest screen settings is about 2.5-3 hours with the battery only being a few months old. Even out of the box with wifi off and brightness down I only got 3.5 if i was lucky. If you need to use it all day without plugging in it looks like you’ll need 2 extended batteries to add to the standard.

mark

Even with screen brightness at minimum and WiFi off, I’m getting 3-4 hours max. And I squint a lot while working.

Raul Ybarra

Got to tell you, I have a tc4200 and if I have the wi-fi off, regular business use gets me a good 5 hours of battery time. When I add the travel battery I’m looking at at… Well, actually, I can’t answer that because I’ve never gone short on power.

With wi-fi on, I’m looking at more like 2 1/2-3 hours. With the extended battery I’ve gone 4+ regularly(again, I’ve never had to push its limit).

My power settings are not very battery friendly- usually Away On, Light sensor off, and a lot of hard disk usage in signal processing. So my times are quite a bit less than a well optimized system would be.

The travel battery does add a pound of weight and I use it mostly when I’ll be in landscape or laptop modes.

Colin Taylor

Not exactly apples to apples but HP also promised approximately the same battery life on the previous TC4200 model. Much to my surprise, when I received my TC4200, the battery life is actually quite close to their projections. I regularly get 4:45 to 5:10 on the bundled battery with the automatic brightness option set and wi-fi TURNED ON! Has actually been one of the greatest surprises of any laptop/tablet I’ve ever used.

Ansin Ozturkmen

They are telling right. If you shut down one core, underclock the other core to 600 mhz, set the brightness to %10, don’t run wifi and bluetooth. While watching the notebook and ask yourself “what the hell i’ve done!”, you will see 10 wh on idle.

jk

Forget the math, a 12 cell battery will add at least 2 pounds to a 4.5 pound device. That is entering Gateway territory. :)

Mark Sumimoto (Sumocat)

Assuming “average” means “normal”, I think you can easily cut that 21W average in half by lowering screen brightness, turning off wireless connections, and going to standby every time you step away from the screen. Stay away from heavy processing, optical drive use, and hungry peripherals, and I’d think it’ll get “up to” maximum battery life. Doesn’t sound like a very productive 16 hours though.

Steve / Chippy

Hi JK.

You’re right with your maths.
and they’re probably right with theirs too.

To get 5hrs and 30 mins from a 55W battery, it needs to take 10W. In theory, that CPU with an efficient screen and good components could easily achieve 10w drain at idle. (If you turned the screen off, you’d probably get more than that too but I guess they draw a line with their creative maths at ‘unuseable’)

Minimum life on the device is probably going to be around 2 hours (playing a big DivX for example)

Table 19 on this doc gives some good info about power ono this CPU.