Do i need to worry about a battery that appears to charge correctly but has a "Service Battery" warning? I have an early 2008 macbook that was running well until a week ago.  I noticed the battery was not charging anymore.  So I bought another battery for $20 on amazon.  I installed the new battery and turned on the laptop.  It was 69% charged on startup - so I waited until it fell to 0% and turned off on its own.  Then I plugged in the adapter to charge it, and although it is charging, I still see a sign that says "Service Battery".  

Do I really need to worry about this "Service Battery" message even though it appears to be charging?
"Do I really need to worry about this" is hard to answer.


If you need to be able to use the MacBook for long periods of time when not plugged in, then yes, you probably do, because the battery that you have is probably not reliable.
If you mostly only use the MacBook when plugged into A/C power, then no, you probably don't need to worry about it at all. It will most likely work just fine for that purpose.


Do keep an eye out to make sure that the battery doesn't start to bulge or anything like that. If it does, immediately remove it from the MacBook.

As an aside: MacBook batteries generally cost somewhere between $80-130, so I would be highly skeptical of the quality of whatever battery you bought for $20 off Amazon. Where by "highly skeptical" I mean "I would not leave it plugged in and unattended when I was not at home." Which is probably me being overly protective, but as the saying goes, "Better safe than accidentally burning down the apartment complex and/or neighborhood."