I installed a battery maintainer. Then plugged it and the blk heater in with the same multi female end 12" cord. This i plugged into an extension cord to house hold current.it seemed to work fine. Later i unplugged the extension and left the short multi end attached to the bliock heater and the battery maintainer on the truck.i drove away. An hour later i turned off the truck later to find no 12 v electrical powerto anything. I unplugged the block heater from the multi block and the maintainer .all was good once again. Question : did i back feed battery power to the blk heater and kill or short the battery while i was driving .i believe they were hooked together because of the multi connector. And also is it ok to both charge the battery and run the blk heater from the same extension cord at the same time. Thanks
