I bought a used 600E from a local computer store. When I brought it
home, it wouldn't boot up. I called the store back and as he had me go
into the BIOS and check a couple of things, it eventually booted up.
This was on the beginning of a holiday weekend. Well, I noticed the
flashing amber light and wondered what it meant, so I went to IBM's
site and downloaded the Hardware Maintenance Manual, to discover this
was the battery light. I then went into the BIOS and ran system
diagnostics. It was showing a problem with the system board. But if I
took the battery out, system diagnostics showed no problem. I came to
find out that the laptop booted fine without the battery, but would
only sometimes boot with the battery installed. BTW, this laptop had
W2K.

After the holiday I brought the laptop back to the store to get a
replacement battery. When they installed the replacement from a second
600E, it fried that battery (at least that is what they told me).
Since they had a second 600E for sale, they swapped out the laptops,
and they went and gave me a battery for it a few days later. This 600E
still works great now.

So my advice is not to put the defective battery in the laptop, and
hope that the charging circuit on your laptop was not damaged.