How to fix a Macbook Pro (late 2013 model) with liquid damage? I bought a refurbished 13" Macbook Pro (late 2013 model retina) from the Apple store website in Sept 2014. It worked great till last month, when I had some water leak out in backpack and get through the ports in the Macbook. 

I believe it has affected the logic board which connects the power port to the battery. When the system is plugged into the power adaptor, it works normal. But, as soon as the power adaptor is unplugged, the laptop shuts down as battery charge can't get going. The diagnostics are showing that the battery should be replaced. 

I took the laptop to the Genius Bar and was told that there is a flat fee for liquid damage repair - $795. I bought this refurbished laptop for $1300 and paying $795 seems quite expensive. I can continue to use it with the power plugged in, but it reduces its usability considerably. Also, once in a while the power cable gets disconnected shutting down the system unexpectedly. 

I called my renters insurance as well, but they did not cover the claim. I may have to just bite the bullet and get it repaired, but I was wondering if anyone has any suggestions on if there are any other options that I have to fix this?
I would say that you would need to go ahead and use the Genius Bar option to repair your computer.

My reasoning is that water damage can cause errors in strange ways that, upon first glance, seem to be straight forward, but are in fact impossible to properly diagnose without professional diagnostic equipment. For example, in your case, I doubt that the problem actually lies in the battery. Rather, the water damage may have caused a part somewhere along the battery-charge monitoring path to fail rather than the entire battery, but that is simply conjecture.

For that $800, a trained technician will take apart the entire Mac and inspect each piece for corrosion and/or liquid damage. Each will be repaired and replaced and then the computer re-assembled and tested and a warranty will be issued for the work. Typically 90 days or the remainder of the existing warranty if any. Local regulations might extend these as well. The only reason this doesn't cost much more than the new Mac is that the parts are not all scrapped and some have repair / reuse value to Apple and they can pass the savings on to you.

Definitely not what you wanted to hear, but I hope this helps.

Caveat: if you can pinpoint that the battery - and only the battery - is the issue without a shadow of doubt, replace it yourself; it will be much, much cheaper.