Cons: High failure rate based on my experience.
I bought a De-Walt Combo Pack that included 2 DC9099 rechargeable batteries. Both Batteries failed within 3 hours of operating time and with fewer than 10 recharge cycles. I purchased a Lithium ion battery and charger to replace the failed batteries at over $110.00. I would not suggest purchasing any DC9099 18V batteries for replacement. The tools in the combo pack have performed flawlessly however the high fail rate of the batteries off set the seemingly great deal of the combo pack. Both batteries went to a dead short and would not recharge even on the new DC9310 multi purpose charger. I would recommend the DC9180 type battery over the older DC9099 battery.