Hi, I’m sorry this happened to you! First, take out all of the battery cells, and then measure them with a multimeter. There are already threads in this forum about reviving cells, see, for example: Battery is not charging - #9 by hartkopp. Fortunately, the battery cells are inexpensive and not very dangerous.
Also, did you upgrade the LPC and keyboard firmware as per MNT Reform: Recommended LPC and Keyboard Firmware Update to fix Battery Drain in "Off" State ? This will avoid these kinds of problems in the future.