How to deal with an IP0R sensor problem?

Greetings!

First, sorry for my so-so english... ;)

I got this A1278 Macbook Pro 13" Mid-2010 from eBay, water damaged, no power (but green light), very clean body, for a ridiculous price... I thought I could give it a shot! It has the 2.66 GHz Core 2 Duo processor.

I disassembled it completely, gently brushed every square inch of the logic board with 99% isopropyl. New battery, new thermal paste... and then, I got chime! Yay.

And then, bam... It just shuts off without any warning. When I hold the power button (maybe 6 or 7 seconds), it will boot correctly. I was able to install OS X, and everything works fine, in fact I'm using it right now to write this post.

3 things are bugging me :

1. It will sleeps, but on wake up, the desktop appears with my apps and the Macbook shuts off only couple seconds after I lift up the lid;

2. I have to hold the power button to POST;

3. When I first ran OS X, the Macbook was very, very slow. I looked up Activity Monitor and a kernel_task was consuming 160% of CPU. I did found a solution on another forum, which was to remove (backup) the file "MacBookPro7_1.plist" (/system/library/extensions/IOPlatform.../Contents/PlugIns/ACPI.../Contents/Resources/). No more slow problem.

So I'm stuck with the sleep/powering up problem. I ran diagnostics and gave me an IP0R sensor error (Charger BMON) reading at 9.166A, which is higher than the high-limit of 8.5A... So, an incorrect current reading. When I boot verbose, I get "Previous Shutdown Causes: -79" information, -79 meaning an incorrect battery current reading.

I'm so close to have a perfectly good MacBook Pro! Please help me, I'm not quite sure in which direction I should go first to troubleshoot this.

Have a nice day and thank you!