how i repaired a FAKE 48 volt Lithium Ion battery

i got a battery operated small pressure washer and it came with 2 48 volt lithium batteries , in fact these were FAKE , battery was 18 volt and 5 batteries missing / not installed , i added another 5 batteries connected in parallel over the existing ones , 18 volt BMS and a 21 volt adapter charge the batteries English subtitles provided