iMac 24 inch 7,1 SOS beeps

An iMac is beeping when switched on. Beeps are 3 short, 3 long, 3 short:

beep, beep, beep, beeeeeeep, beeeeeeep, beeeeeeep, beep, beep, beep

Basically SOS

So far I've tried:

1. swapping RAM with working computer
2. swapping power cable with working computer
3. holding down D and other keys

Looks like its a EFI ROM corruption. Could possibly be the battery. Will try replacing the Battery first. Here's a tutorial on it