This is the first symptom of deterioration of one or more of the battery cells. Generally there is a decrease or increase in the battery charge without apparent cause in small percentages, and over time the jumps in the charge become larger. It could also be due to an imbalance in the charge level of the different cells without any of them actually being damaged. What is strange is that it happens after a year of use. It usually happens after two or more years, but you have to take into account not the time of use but the time from the moment the battery is manufactured, when the battery life counter starts. Lithium ion batteries generally have less life than lithium polymer batteries. I don’t know what the prime’s is. I have been using the Kospet prime for 18 months and so far the battery is perfect. The solution lies in a battery replacement, and I don’t know if Kospet sells spare batteries.