MacBook only works when power adapter is plugged in

Battery seems to be faulty, there are 2 values well out of standards:

• voltage is not supposed to be 5v. but 8v. There’s some tolerance downwards but 5v. is much too low to keep the machine up and running.
• Capacity is suspiciously on the high side. As you can see it reads 16,400mAH. A typical value should be around 12500mAh. I can understand some seller might set theorical capacity a bit higher, but this seems a bit too much.

However, even if we take capacity off the picture, voltage on its own says it all.