T616 Water, corrosion damage

A while ago my battery started to only hold a charge for 2 days, eventually
I sent it in for warranty and it came back not qualifying for repair because of water, corrosion damage, this likely from being splashed or rained on briefly. I put a new battery in and it didn't help and the phone still appears to be working properly. Anyone know what the problem is? or know what part needs to replaced as well as a good source? cost?
Instructions for taking it apart, also helpful, being told they can be difficult to take apart. Is it worth it the cost, bother? I was going to try cleaning first.

how did the battery get wet?

The best I can remember, Either from walking around outside in the rain with it in upside down in my pocket or splashed on while washing my face. Once possibly from being to close to the sink while hanging from a lanyard.
I don't believe it was ever immersed in water and it's in a case with the lower contacts, plugins exposed.
I was also having a problem getting the charger to fire up and eventually looked at the contacts on the phone which were dirty, On cleaning them the problem with the charger contact went away, bit the level of charge remained the same.

I found some instructions for disassembly in another forum, took it a part and found a small amount of corrosion on the power, charging contacts, cleaned them and put it back together.
In 48 hours it still had 3/4 charge so I have in back up and running now. The only problem being a couple small shadows, dark spots on each side of the lower screen. Likely caused from handling or over-spray from the aerosol cleaner I used. I also broke a plastic tab off a corner of the screen frame, but it didn't look like it was important and still went back together OK.