Not really practical or safe. If the car battery charger has a current limited mode that is substantially bellow the pack capacity you might be able to monitor it with a multimeter but it would be extremely unsafe if you don't know what you're d oing.
There IS a charger for what you want. I'd start at Radio Shack ( in stock or can be ordered) then ask at places like WalMart, Office Depot, etc. There are chargers for almost anything, it just takes a few phone calls. OR call a Hobby Shop, chargers for RC 'toys' like I have.