Think Howie is onto something. Also, if they are still orig batteries, the odds are they are beginning to fail. In addition, the converter in these units cook the batteries. Should you need new batteries or a new converter, go with a 3 stage charger as found at bestconverters.com
Did this with my unit before I replaced the batteries. Takes about 30 minutes to swap out and about $200 in cost, but will keep your batteries in good shape longer.
Computers manufactured by companies such as IBM, Compaq and millions of others are by far the most popular with about 70 million machines in use worldwide. Macintosh fans note that cockroaches are far more numerous than humans and that numbers alone do not denote a higher life form. -NY Times 11/91