Draining only a single battery?

I was experiencing sudden shutdowns, after which I could only boot up again by plugging in external power. Once rebooted, the battery charge level was nowhere near 0% and this was happening too frequently.

I got curious this morning after another episode, took out the batteries and put then in a charger. The charge level meter says one is completely drained, but the other is near 100%.

Anyone experienced something similar? Would this be simply a matter of insufficient contact?

I have the same question´╝îafter my test, I found that the batteryboard and the metal sheet of the mainboard do not contact well