The regular charger will work, it just takes longer to do the job.
You can get a charger for $18 that is good for overnight charging of higher capacity packs
http://www.maxxprod.com/mpi/mpi-9.html
Scroll down and find item CH96
Universal, Rx 4.8V/180mA & 6V/150mA, Tx 9.6V/120mA