My iPhone 4S battery was weak, as in if I remove the charger after it's fully charged it would go down to 99%. I also jailbroke my phone just to check the batteryinfolite and to my surprise, my battery health was at 90% out of the design capacity at 73 charge cycles, which I consider weak.
Repair went pretty quick. Less than 10 minutes. although removing the battery was hard but I managed to get it out.