Most likely that is going to be a battery problem. You have plenty of volts but insufficient Amperage to turn the motor over indicating there is a Dead cell in the battery you currently have. The problem with these smaller batteries is they develop memory quickly and don't respond well to being left on a charger year round when that is done. When stored the best way to maintain the battery is to find a way to put it under a load every couple of months and then recharge. Simply connecting it to a charger or allowing it to sit on bare concrete, even during charging, is bad for lead based batteries. When not installed on the vehicle it should be stored on a piece of wood to prevent ground contact or grounding.