I have the d3400, bought it used about 6 months ago. Worked fine up till about a week ago. After only sitting for acouple mins it drops to 11.3-11.6. Bought the ctek 4.3 charger charged it overnight. As soon as i unhooked it in the morning it stared falling to 11.5. Is it done or can i save it to use alil longer. Thank you for your time