Battery Help 3V vs 3.7V

[glammdan]

I have an older palm device that I have been wanting to use more, but it just eats up AAA batteries. I thought about buying some rechargeable AAA, but I want to try to maximize the amount of hours I can use it. I have been thinking of trying to put a better capacity battery (like a rechargeable lithium-ion), but the voltage is 3.7 Volts. Would the extra  amount of voltage be harmful, or is it to small to hurt the device? Any advice will help.

[Simon]

"old" and "new" batteries are the same voltage as always, I don't see you problem

[glammdan]

Sorry, I guess I didn't make myself clear when I wrote this. The device uses two AAA batteries in series. The sum voltage of the AAA batteries is 3 volts. I want to use one rechargeable Li-Ion battery (like this one http://www.dealextreme.com/details.dx/sku.30996) , but my problem is it's 3.7 volts. My question is, will the extra .7 volts hurt the device or not? Sorry for the earlier confusion.

[Simon]

possibly, you masy want a higher voltage battery with a SMPS to reduce it to 3 volts

[Zero999]

You can buy rechargeable AA batteries with a capacity of 2700mAH.

[OLSA]

That 3.7V is nominal voltage for that rechargeable Li-Ion battery, and after charging would be ~4.2 V. In palm you have DC/DC voltage converters and they produce 1.8V, 2.8V, 3.3V etc...and that's max. input voltage depend on type of converters (like input voltage 2.8-5V/output 3.3V; or different input 3V/output 5V etc...)
Better try to find some rechargeable AAA batteries like NiMH 900-1000mAh (Sony, Sanyo...).

[Zero999]

Oh I've just noticed, you said AAA, not AA, so you're limited to 1000mAh.

Perhaps you could use the Li-ion and a small low drop-out regulator?

[charliex]

which palm device?

[Brett]

If it "eats" up AAA batteries, it probably draws a good bit of current.  An LDO is going to be hard to find that will go very high current wise... your best bet will probably be a 3V output Buck regulator with the 3.7V Li battery.  You may have to use a SEPIC type of converter if you need more headroom though.

Why not just save yourself the trouble and get an iPhone?  Then put all of your effort into something really useful...
(sorry, had to say it... don't kill me)

(I might be an iPhone user)

(ok, iPhone pwnz all!!!!!!)

[Simon]

how about using more than 3.7 volts ? if your using a DC/DC converter that is efficient it may work out better than trying to use the :DO or find a very specific device to drop just 0.7 volts, of course you may well get away with 2.8 volta output ?

[glammdan]

 The device is a palm IIIxe. I bought it a while back for 2 bucks at a second hand shop, brought it home and found out it works great (except for the aforementioned battery problem).

I have been thinking about a regulator, but thought that if I could do it without then I would.

I have no problem using a higher voltage, just as long as the battery would fit inside the device and wouldn't cost too much.

 the problem with using AAA batteries is that most rechargeable AAA batteries probably wouldn't last as long as the Li-Ion batteries I have looked at, and the good ones cost a lot (remember 2 dollars at second hand store).

(If I had found an Iphone in a second hand store for $2 I would have bought it.)

Thanks again for all the help.