I would recommend a new battery.
*PS DO NOT USE a cheap Ebay screwdriver those screws strip VERY easily and are near impossible to remove otherwise.
Replace that dying battery or carry an extra for backup power! 3.7 V, 5.3 Whr, 1430 mAh. Compatible with all iPhone 4S models. — 10 available at 24.95 each.
Standard Phillips screwdriver used to take apart laptops. Swivel top handle with precision tip driver. — 50+ available at 4.95 each.
Compatible with the type 5IPR fasteners used on the iPhone 4/4S and iPhone 5. Swivel top handle with precision tip driver. — 50+ available at 11.95 each.