FROM HP:
Your iPAQ Pocket PC h5400 Series has a built in safety feature to protect the battery from over- discharge. This feature is necessary in case the iPAQ is left without A/C power for an extended period of time with the battery installed. When the iPAQ h5400 battery depletes to a critically low state, the iPAQ will not power-on nor will it visually indicate it is receiving a charge until the battery is charged for a specific amount of time. Your battery will not become damaged when this situation occurs and no performance loss will be experienced.
When the main battery depletes to less than aprox 20%(?) or lower, the backup battery 'failsafe mode' activates and prevents the unit from turning on until recharged and soft reset(ed). This feature is badly documented which would explain why so many people were getting frustrated with thier iPaqs, hence the reason why the documents came out late. Also the
'BETA' battery patch HP released attempts to address the very problem you describe.
FROM HP: 'RESOLUTION'
[b]Connect your iPAQ Pocket PC h5400 Series to A/C power and wait a period of 5 minutes (*see note below).
After a sufficient amount of time has elapsed (with A/C power connected), perform a Normal Reset.
The device will power-on and you may follow the instructions to set-up the iPAQ Pocket PC.
Allow the battery to fully charge before using the iPAQ Pocket PC.
http://wwss1pro.compaq.com/support/r...=3&docid=16201