You have a bad cell. Time for a new battery. The vendor that supplied the cells for the G751 Series machines has had a pretty high failure rate. If you use the search feature you will see no fewer than 100 threads with the same problem.
Food for thought
These machines are not in any sense of the word a laptop, they are huge heavy desktop replacements with battery life that even when good is bad. They are meant to be used plugged in.
These batteries are not Nicad. They do not form a memory, you do not need to disccharge them then recharge them. They are lithium polymer chemistry, the only thing on the market capable of putting out the required power to run them. Every time you do a discharge that is one less discharge you have on the batteries lifespan.
“Two things are infinite: the universe and human stupidity, I'm not sure about the former” ~ Albert Einstein