2008 MacBook (A1181) won't boot from battery I have a 2008 13&quot; (2.4GHz) white MacBook that will only boot from mains power.  If you attempt to boot from the battery it's as if it's not even connected.  Once you get even past the initial startup chime, you can pull the mains and it's fine.
Things I've tried so far

Replaced the top case (as I had to replace it anyway)
Removed the top case and used the power jumper.
Checked battery status (4/5 lights)
Checked magsafe light status (Orange initially, green after a short wait)
Ran diagnostics (which only reported 4SNS/1/4000000 Th1H-128.000... - a temperature sensor error)

I'd appreciate ideas on what's causing this when the battery clearly has (and can supply) power and more importantly how can I resolve it?
So the fan doesn't even spin up when attempting to boot from battery?

First thing to try is resetting the SMC:
http://support.apple.com/kb/ht3964

Any chance you can try with another battery? Although from what you've described it sounds fine. You might be looking at the logic board as the fault.