Why, oh why, do people try to skimp on the charger?
Lead acid chargers are absolutely NOT suited to charging lithium. End of story!
A lithium charger is a very simple device and should cost no more than $100 for a 10 amp example.
The correct charger will enable you to get the most out of your lithium battery investment, both with run time and pack longevity. You will not get the long term life out of a lithium pack that is not charged correctly. So not spending the $100 now will cost you much more in the long run.
Cheers
Pat.