Hey Alex,
I just updated my macbook pro 2008, to el capitan, and everything was fine for a few days, till yesterday when exactly what you mention started happening. Although now that I read through the symtpoms you've mentioned, I do recall odd fan behaviour, that would happen on and off, but never thought much of , since everything else was working fine.
Have any of the above mentioned solutions worked for you?
Because I too am out of warranty, with the same led flash 5 times, battery not charging, sleep indicator blinks few times on startup.
Any help would be fantastic, because I am about to attempt one or more of these fixes mentioned here.
Fingers crossed.
Thanks in advance
Nigel R