I have a 52 volt battery, when I charge the battery fully and check with a multimeter it always shows me 0.2 volts less instead of 58.8 58.6, the same with when I charge to 85 percent instead of 56.6 56.4, I built the battery in 2020, with batteries of production date 2018, the question asked For those who understand batteries, is it normal for a battery at this age, when should I be careful/change the battery? Because the battery is working properly