Every time i turn on my sony cyber-shot DSC-N2 now it says "For use with compatible battery only" and then turns off? Never happened before in last 4 years of use? Any suggestions... maybe need a new battery?

Your camera uses a proprietary Sony InfoLithium battery which I presume you are using. The message normally only comes up when using non-genuine batteries though the chip in genuine batteries sometimes gets corrupted. Four years is a fair lifespan for a rechargeable lithium cell so even without any faults you may already have noticed that the battery needs recharging more frequently.

Check that the battery contacts are bright and clean, and use a torch to look inside the battery chamber to check that the camera contacts are intact and clean. If all checks out then borrow or buy a replacement battery. If you buy a battery then you'll have to try and resell it if the camera proves to be at fault.

If the ultimate conclusion is that the camera is faulty, then it's cheaper to just replace it rather than repair. It was only designed for a minimum five year lifespan, so if it's failed prematurely you've been a bit unlucky. It's worth complaining to Sony anyway, but as they'll want to inspect the camera and will charge you for shipping with no guarantee of a favourable outcome you may decide that you'll just be gambling more money which could go towards a replacement camera.