Might be a dead battery?
I've had it on trickle charge for 24 hours - but the headlights and rear lights flash 5 times every 20 seconds or so.
I've googled this and nothing comes up.
WTF??

 

Why do you suspect a dead battery?, A car w/ a low battery generally won't waste power by flashing lights.. Trickle charging is really meant to maintain a full charge in a battery, not "recharge" a dead one. Your lights are probably burning up whatever you are putting in.
Sounds similar to an alarm being triggered by opening a door from the inside when they are locked. Have you tried the deactivating procedure?



BTW - if that is the original battery I'd change it, if it's not dead now it soon will be.

 

+1

 

What is the de-activating procedure? And why would that help?

 

Alarm – turning off The alarm system provides a warning if an attempt is made to break into the vehicle. If the alarm is sounding, it can be stopped by pressing the Unlock button on the remote key or by inserting the remote key in the ignition slot. Two short flashes from the car's turn signals confirm that the alarm has been turned off.


I think Volvo alarms do what they want, when they want. I recall that my son called me once with his lights fglashing like crazy, no siren and he couldn't start the car. Hit the LOCK then the UNLOCK buttons a few times and all was well. This morning I simply opened my S80's trunk and the siren and lights went off. Again, LOCK / UNLOCK and the siren and lights went off. BUT when I tried to start it twenty minutes later , it wouldn't and the little red dash light was blinking rapidly. I finally pressed the interior door lock and then the fob unlock and all was well. I have no idea why.