Love my Ryobis- have 18V driver, 90degree drill, circular saw, reciprocating saw, and flashlight + 2 batteries. Also have a corded router and orbital sander. Good enough quality to do occasional jobs, priced to not break the bank.
Not sure about lithium batteries, but I know that if some batteries become discharged too far, the charger will not charge them, so the batteries can be 'jump-started' to bring the voltage back up to minimum for the charger to recognize them.