z50 battery oddity

I got out my z50 today, and it wouldn't turn on.  So I plugged in the
mains brick/charger and it then would, but it was acting odd: the
battery light (normally off when on battery, orange when charging,
green when charged) was blinking between green and orange (rough
estimate: .5 sec orange, 1 sec green, repeat).  Listening closely in a
quiet environment, I can hear a soft click when it switches from green
to orange and a very slight high-frequency noise while it's orange.
The click sounds like incidental mechanical stress from an electrical
change, not a mechanical switch.

It booted apparently normally and I was able to do what I wanted to do
(see if a PCMCIA card I dug out of an old box-o'-stuff did anythiing
useful).  While I had it up, it seemed to flip between battery state
critical and battery state high randomly (according to the kernel
messages), and, no, I'm not running any kind of non-kernel power
management software.  (The kernel in question is 3.1.)

I tried removing and replacing the battery; this made no apparent
difference.  Pulling the AC power plug produces an ungraceful shutdown
which produces a cold boot when I next wake it up.

Any ideas?  Is my battery toast?  It was fine last time I used the
machine (I put something like 30-60 minutes of run time on it; it
normally has given me about two hours of run time on a full charge).

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