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

Tc4400Warner 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?



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