XPS 13 L322X: battery capacity drop

Hi,

I have a dell XPS 13 L322X that I bought in 2013. Recently I bought a new cooling fan because the original one was very noisy. However, after replacing the cooling fan, I noticed that the battery capacity dropped to less than 10%. Therefore, I decided to buy a new battery. The problem is that the capacity/health of the new battery dropped to 75% in just a few days. I contacted the seller explaining him the situation and he sent me a new battery; however, the new one has already lost almost 50% of its capacity/health in just three days. One thing that I noticed was that the (second) new battery has an Energy (design) of 50,2 Wh whereas the original one and the first battery that the seller sent me both have 47 Wh. Another thing is that while I was calibrating the battery, in the first cycles, the battery was charged only up to 90% and that the capacity loss happens after a reboot: in the end of a cycle there is a decrease in the battery capacity after a reboot. After a reboot, the system shows the battery is fully charged, but with a decreased capacity. Every single cycle the capacity drops. The XPS 13 is running Ubuntu 16.04. Would you have any idea why that’s happening?

Many thanks.