Lee Fot,

How old is the unit?

This seems like a classic battery failure pattern.

As the battery ages, the energy storage capacity diminishes, requiring more frequent charges. Simultaneously, the battery seems to charge much faster.

On my cellphone I go through this about every two years, almost to the day. (I keep phones for a long time). After a few minutes of operation, the battery appears to be completely discharged, yet it will recharge in a few minutes, rather than about 14 hours. Normally, two hour conference calls are not a problem for this phone.