High-current output batteries for secondary power supply

[jaem]

This is a continuation of the subject matter discussed here.

My Palm's battery lasts a fair while, but one issue is that it has automatic wake-up whenever a button is pressed - and the buttons aren't recessed. Thus, several times a day, I have to check and see if whatever I was carrying brushed my hip and turned it on. This wastes a lot of power, and as I'm running a development version of Linux on it, I'm not sure what I'd need to mess with to change this.
I want to know what's out there in terms of batteries that I could use as an extra power supply (e.g. to plug in to the power socket as if it was a charger). The parameters are as follows: The battery has to be able to fit in a nice leather beltclip pouch, to match the rest of the gadgetry that I'm accumulating; it has to be fairly cheap (e.g. student budget) and easy to get (e.g. not ordered from Antarctica); and (here's the tricky part) it has to be able to supply at least 0.51A at 5V. I can use a switching reg if need be - heck! I can get them free anyways. The datasheet for the charge controller inside the Palm lists max charging current as 1A, and so does the sticker on the back of my Palm, but I've used the Lab power supplies to charge it fully, and never had it go over 0.51A. Because of this, I'd be fine with a protection circuit and a cheaper battery.

The charging circuit is inside the Palm, so all I need is a voltage source - in this case, a rechargeable battery.

The last parameter is that I need something that I can get or build a charger for for cheap. I don't trust myself to build a Li-ion charger with my present skills - I don't want it to blow up on me!

Any ideas?

[jwax]

Strap on a 4 pk of 2500 maH NiMH batteries.

[jaem]

...is that all it would actually need? I was under the impression that they wouldn't like me drawing half an amp...

[jwax]

In theory, you'll get 5 hours of a half amp. That's 1/5 of the Amphr capacity- yes a high discharge rate, but remains to be seen how much of a charge that is in the Palm.

[zotdoc]

not to be overly simplistic, but get a case to put the thing in that will keep the buttons from being pressed by accident. I'm not sure that you would be able to take the automatic wake up feature out without taking out the automatic sleep after 45 seconds feature, and that would not be a battery saving move.

[jaem]

Zotdoc -- That's not really a viable solution. I had a really hard time finding any case that would fit my Palm (Zire 72) in my area. I finally found one that fit from HP for a good deal ($20 for a nice leather one), and I can't return it now.
Also, I'm using Linux on it, so I'm quite sure that it would be possible to turn off that feature - it might just be difficult. At any rate, I would like to have a secondary battery anyways.