Battery status is showing vague percentage on apple devices

I have powerbeats 3 wireless from last 2 years. I had to replace it once in warranty due to ON/OFF problem. The new pair was working perfectly till last week. It stopped working suddenly. After opening the cover for battery I noticed oxidation on the solder portion on P-. I had re-soldered the battery and fixed the cover. The device is working fine but the major problem I am facing is, it does not charge completely even after 2 hours. When I turn it on, it shows random battery charge values. Most surprisingly it shows different values on different apple devices. Ex. iphone shows 23%. If i connect it to my MAC, it shows 3%. Again if I connect it o iphone it shows 27%. I am not sure how it measure the battery pct. Yesterday I noticed that it was showing 18% battery, it worked well for 1.5 hours showing 5% battery for last 30 min. Is there any easy fix for this? While soldering the cable from the device does not look in great shape. The strands are spread in some cases. I tried my best to tin the strands.