disclosed are various circuits which assure safe connection of battery chargers or other electrical apparatus , wherever two sets or pairs of terminals are to be connected safely . additionally , overload protection modules and on - time delay modules prevent overloads from being transmitted to the receiving side and delay the connection to the end terminals . further , a minimum charger - voltage - detector version prevents use when not safe . various embodiments of circuit modules , including using a micro processor , are presented in accordance with the invention .