MacBook Pro - won't boot up beyond grey apple?

Never seen this before.

When booting my MacBook Pro the screen shows the grey apple and the little boot up spinner, but also a loading indicator bar across the bottom. The spinner spins, the indicator bar fills, then disappears, but we never actually boot up ... just stay grey and spinning.

It's been running fine. The only thing I can think of ... the battery is not holding much of a charge any longer. Last night it died while still indicating 80% charge. It's been dying without warning at 30%, then 50%, now only a few minutes after I unplug the power adaptor.

Is it possible that the fact it won't boot up might have something to do with the battery no longer holding a charge? Tell me I can go and get a new battery and everything will be all right....

My DiskWarrior is 3,000 miles away.

Is there anything else I might try?

I'm in the middle of some business negotiations that I've been doing mainly by email ... didn't write down phone numbers ... could I pull the hard drive from the laptop, stick it in an external bay I have here, and open it with an iMac, to be able to access my email? Given the problem isn't the hard drive itself or course.

Would there be a specific protocol for opening an app installed on an external drive? Like Mail for instance?

All ears,

Ben