Battery issues on my Thinkpad X1 Carbon 5th Gen

Hi,
Does anyone know why the battery on my X1C (5th gen) suddently goes from 20% to 5%? I only replaced it last year (genuine Lenovo one) and its only been through 160 charging cycles. Also why would the battery capacity go from 57Wh to 48Wh in less than a year? I mainly use it on battery power and once it falls below 20%, then it charge it to 100% and remove power supply. Battery display gauge has already been calibrated using the Lenovo utility.
Thanks

 

I don't think a 15% reduction in capacity with a high cycle count is particularly out of the ordinary after a year. I seem to recall the modular battery on my R60 after a handful of uses being at less than 50% after six months. Due to the chemical properties of batteries, they degrade over time. There's no getting around that at this point in time.