12volt dc input to charge an 18 volt cordless tool battery

I have a purpose built 24 volt dc output/ 12 volt dc(cigarette plug) input for a cordless tool battery. a WALL WART version is quite expensive by comparison. Can I use 24 volt dc as the input voltage to use with this charger. I have 1 300ma, and 400ma ac/dc wall warts that are used with two other chargers, both 24 volt dc output. all are the same brand and basic design to be used with the same battery. this would avoid needing yet another charger. my two wall wart chargers were replaced. the dc /dc charger would be helpful if I could run it on 24 volt. answer please.