I recently purchased a SX3000-30 walkie stacker via industrial auction. The unit was moving around about 2 weeks ago but now it appears the batteries are dead. When plugging in an extension cord to charge, there are no lights. Did a search on this forum and it points to the possibility of the batteries being too low for the internal charger to kick on

I have a few 6v capable chargers. Is there anything special that needs to be done to remove the 4 6v batteries? I can only see two at the top but I'm assuming the other 2 are below. Any help is greatly appreciated. THank you