Ben CombeeThe Foleo's battery is identified as Palm part# 157-10039-00, a li-ion battery with rating of 7.2 V and 3500 mAh. It's a 2P2S configuration - the type is LP103450SP-2P2S. All of my battery packs have self-discharged into a unrecoverable state, and no off-the-shelf alternatives are available. Physically, it looks like the Palm engineering team took the cells from four Treo battery packs (3.6 V, 1750 mAH) and wired them up in a 2P2S config.
The connector to the main board is a set of five contacts arranged as
1 - Vin
2 - plastic pin
3 - ???
4 - ???
5 - ???
6 - GND
From testing with a bench power supply, I'm able to power a unit with 7.2V applied to Vin and ground connected to GND. The unit would act as if it was low battery from 6V to 7V, with no LED blinking at 5V. I don't know much about the charging circuit; there's an adapter input on the side of the Foleo which provides 12V 1.5A with a center-positive barrel jack. With no battery installed, this power circuit is sufficient to bring up a Palm logo on the screen, but some early system check fails and the device resets.
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One of the three ? pins is likely going to be a thermistor pin, on the connector, there should be a resistance from that pin to GND - anywhere from i.e. 100K to 1K, I'd guess, it tends to vary a lot from one manufacturer to another =) It should be easy to locate this one with a multimeter with the resistance measurement mode! As for the other things, there's basically four options. It's possible that one of the pins is simply a pin that prevents battery from outputting any kind of voltage until it's brought to a certain state, as EEE PC 701 does, for instance - you need to short one of the pins on the battery to battery's GND pin to have VBAT on the connector. Another pin could then be some kind of one-wire transmission pin for the internal fuel gauge. Or - two of the remaining pins could be SMBus (I2C) pins, one SDA and one SCL, in case your hardware team opted for a SMBus-connected fuel gauge battery =) And, of course, one or even two of those pins could just be NC =) A thermistor pin is one pin you're most likely to find, statistically. You can only be 100% certain if you do some motherboard reverse-engineering, or get access to the motherboard schematics and check the signal names, but a bit of logic analyzer probing with a $5 LA is nigh-certain to make it all clear enough for most purposes, given that you do seem to have a working system.
Also, I'd be careful powering the system from both the battery input (using a PSU) and the 12V input - it's not a certainty, but if the AC and the battery are both present, the system might try charging the battery, which might result in a current fight or something. Powering it from the battery input alone should be safe, though - I've powered a Palm Tungsten E2 that way, pretty successfully =)
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