Hi Mike,
 
Thanks for getting back to me!
 
Yes, I plan on a custom Li-Ion pack for power.  I really want to be able to run for over 8 hrs a day without recharging.
For that kind of power, Li-Ion is really the only answer.
 
Dan


----- Original Message ----
From: Mike Morley <mjm80@cam.ac.uk>
To: Dan Brown <dan@lantzer.org>
Cc: balloon@balloonboard.org
Sent: Monday, August 21, 2006 5:05:30 PM
Subject: Re: [Balloon] Balloon 3 Questions


> 5.  How are they looking as for as power usage is concerned?  (My 
> application is in wearable computing...)

I can only really answer question 5 from our experiences here at CUED. 
Typical current draws are 100-200mA, and we're developing three 
different battery technologies:

For robotics within the department, ~2.5AHr batteries at a nominal 12V:
  - NiMH pack - lighter, but considerably more expensive. We're 
currently experiencing problems with our charging circuits.
  - Sealed Lead-Acid - heavier, but around 1/3 the price of the NiMH 
packs. I've got a working demo sitting on my desk, and am currently 
routing a small PCB.

For the PDA being developed, we obviously had to go with Li-Ion for the 
weight saving, and - for convenience - I selected the Nokia BL-5C 
battery - 900mAHr at 3.7V. The beauty of these are we can run them in 
parallel to get almost 2Ahr, and they're easy to charge -- either in a 
Nokia desk charger or a phone like the 6230i (Which both I and Chris 
Jones have)

I hope that's of some help - I imagine for wearable computing you'd want 
to save as much weight as possible and go with Li-Ion (even the NiMHs 
weigh in excess of 0.4Kg


Mike Morley