What was found
DURING TAXI OUT,LE SLAT ASYM CAUTION MSG AND LIGHT ON AFTER START CHECKLIST. SEEMS TO HAPPEN WHEN SELECTING APU OFF WHILE FLAPS ARE IN TRANSIT.A/C RETURNED TO THE GATE AND MTX GROUNDED A/C MTX T/S LE SLAT ASYM MSG PER B767 FIM 27-81 FT 809 FOUND MAIN BATTERY INOP REMOVED & REPLACED MAIN BATTERY CHARGER IAW B767 AMM 24-31-02 OPS CHECK GOOD. CYCLED SLATS ON APU & ENG POWER PER B767 AMM 27-81-00. NO FAULTS NOTED. AND RETURNED A/C TO SERVICE.