I am wondering about the condition of my phone, VX4500

I was at work last October and I dropped the phone in a bucket of water.
It was completely submerged for about 4 seconds,

I pulled it out and removed the battery and proceeded to take it to the bathroom and blow dry it...

hours later I put the battery back on (the red sticker on the back indicating water exposure was activated) and I turned the phone back on.
the screen came up and it worked for about 5 minutes before turning into a white blur, and then powering down,

I got just got a new phone and they took the numbers off the one I dropped by removing a small plastic cover on the face of my phone and plugging into it,

I broke the new phone and got an old old one for free,.. it's circa 1999...

I charged up the original phone, the one I dropped in water, and when I turned it on to my surprise everything about it was working perfectly the speaker phone, the recorder, the ringers, the screen.

So I got the contacts I needed off of my original phone and a thought occured to me, to test the phone and see if it was still viable for use.

I charged it again and left it in my car and a week later it still worked to my surprise, everything perfectly,...

However, Everytime I open the lid to use anything, the battery instantly loses like two power bars when I close the lid they come back, but phone would be closed with 2/3 power and I'd open it and do stuff with it and within minutes a "WARNING charge low battery" message will pop up...

I am just wondering

1. is the phone still usuable?
2. is the problem exclusively the battery, or could there be a problem with the phone as well?
3. If I replace the battery will the problem be solved?
4. any suggestions?

I know I could go to verizon and ask them personally,...
But I don't want to get up and drive there, and I'm bored, this is killing time lol,... so please get back to me,...

I suggest simply changing the battery, since that's what seems to be the problem. You say it works perfectly, other than the battery, so chances are that's the only problem!