Corrupt power manager settings can cause all sorts of troubles – including the failure to recognize batteries in some models, but as I understand it, this is owing to software in the power management system rather than juice in the backup cells per se.
My advice, having worked on these a fair bit over the past year, is to reset the power manager as per Apple's instructions; if it doesn't then immediately recognize the main battery after the reset, it's most likely a defunct main battery.
For real use rather than an idle tinkering once every 6 months, however, you would likely want a working backup battery, even if the main battery were good. I have a 280c with a dead backup battery, a 270c with a working backup battery, and a 2300c with a working backup battery. I have two working main batteries between them. Even with the best of the batteries installed, there is a world of difference between the three: the 280c exhibits random problems that I put down to the dead backup battery. Failure to recognize the main battery is not among them; glod and random shutdowns are more the thing, but the problems are so persistent that they make the machine unusable. I put the 270c and the 2300c to good use for some writing projects over the past year, and they were both rock solid, and very portable in a briefcase. I couldn't have used the 280c because of its erratic power-related behaviours.
My advice, having worked on these a fair bit over the past year, is to reset the power manager as per Apple's instructions; if it doesn't then immediately recognize the main battery after the reset, it's most likely a defunct main battery.
For real use rather than an idle tinkering once every 6 months, however, you would likely want a working backup battery, even if the main battery were good. I have a 280c with a dead backup battery, a 270c with a working backup battery, and a 2300c with a working backup battery. I have two working main batteries between them. Even with the best of the batteries installed, there is a world of difference between the three: the 280c exhibits random problems that I put down to the dead backup battery. Failure to recognize the main battery is not among them; glod and random shutdowns are more the thing, but the problems are so persistent that they make the machine unusable. I put the 270c and the 2300c to good use for some writing projects over the past year, and they were both rock solid, and very portable in a briefcase. I couldn't have used the 280c because of its erratic power-related behaviours.