We purchased a system called power in a box for our conversion van. Due to some circumstances we have not been able to use the power in a box and we are unsure of how to store the (3) 200ah Victron lithium batteries. They have been in our storage area for about a year now. We have never plugged them in to use. Can we continue to store them just as they are or should they be plugged in occasionally to charge? If so, what charging unit would you recommend? Thank you very much!