I have purchased two used SV21-30008 carts with battery power. They work great until the battery runs down (still showing 56% in the ICP and after 1to 2.5 hours on battery) and then after pluging them into a UPS they will not charge the battery again until I lay it on its side, remove the retractable plug module (aka the battery door), and un-plug and re-plug the blue/green/red battery leads block (I also press on the reset buttons for the three circuit breakers). What gives?? I've synchronized the ICP by letting it charge overnight and pressing the two outside buttons. Also, the light on the inverter changes from solid red to blinking red even though the switch is still in the "on" position and not the "stand-by" position. Batteries are good ones. Does anyone have any idea or suggestions as to what to do to fix this? I have also replaced the plugs, thinking that perhaps a wire inside had broken due to repeated retractions of the the cord. HELP!!!