trimming leading characters
SELECT to_number(replace(DESCRIPTION, rtrim(DESCRIPTION, '0123456789')))
FROM   PART
WHERE  PAR_ID=123
AND    DESCRIPTION LIKE 'CHARGE BATTERIES%';


When there is no number at the end it will result NULL. If you want to have zero then use:

SELECT nvl(to_number(replace(DESCRIPTION, rtrim(DESCRIPTION, '0123456789'))), 0)
FROM   PART
WHERE  PAR_ID=123
AND    DESCRIPTION LIKE 'CHARGE BATTERIES%';