Macbook 5,2 (mid 2009) doesn't recognize battery

Hi,

I have a Macbook from mid 2009 and suddenly shutdown and doesn't turn on with the battery, only with the power adapter connected. The battery is connected but not charging.

I reset the SMC and NVRAM but seems to be a firmware problem. Then I saw this firmware upgrade ( http://support.apple.com/kb/DL1625 ) that may solve this issue, yes, my battery have more than 1000 charge cycles. But the installer doesn't allow me to install it.

Any thoughts?