Determining why your brand new cell phone battery is not holding a proper charge begins with identifying the battery type and understanding the factors that can affect it.
Nickel-Cadmium (NiCD) Charging Issues
Although this battery technology is older, you may have purchased an entry level phone that was never used and comes with an NiCD battery. Nickel-Cadmium batteries are prone to a condition known as "memory effect" that causes the battery to believe it only has as much charge available as the last charging point. For example, charging the battery at 50% will make the battery think only 50% is available. You should allow the battery to charge for a full 24 hours, then use it until it completely runs out of power. Cycle the battery using the 24 hour method three times and then repeat the 24-hour charge and full discharge one time every 10 uses. This "power cycling" helps reduce memory effect.
Nichel Meta-Hydride (NiMH)
This battery's charge can be damaged if the phone is used in very low temperatures or if the phone is charged in sub-zero temperatures. The battery also delivers a low "load," meaning a bright backlight on your phone's screen that is constantly in use can damage and quickly drain the battery.
Lithium-ion batteries operate more poorly at low temperatures. Temperatures below freezing can cause the battery to lose its discharge levels and sputter out more quickly. BatteryUniversity also suggests that while these batteries do not suffer from memory effect, they should be fully charged and discharged every 30 uses.
Charge Times by Battery Type
The time required to charge your battery depends on the battery type (NiCad, NiMH, Lithium) and its size. For example, batteries are measure in milliamps (mAh) with 1500 mAh being much larger than 800 mAh. Consult your user manual or the manufacturer's website for charge times.
Even if your phone is in new packaging, the battery may be expired if the phone is an older model. According to Microsoft, the average Lithium-Ion battery only has a shelf life of two to three years. This expiration occurs whether the battery is used or not.