12v Battery power is from full charge, About 14.8v to 11v.
Any lower or higher can damage the battery.
Some batteries cannot go as high as 14.8v and some can go lower than 11v.
Why my new battery won't hold a charge?
1) Your battery might be loose. Please check the connection between the battery and the device to be sure the battery is securely attached.
2) Some devices come with multiple batteries. You may also want to try to charge an alternative battery in the device or charger. If you have already checked both of above and still had troubles to charge the battery, either your battery or your charger/device should have problems.
Why my new battery has a very short running time even "fully" charged?
New batteries are supplied in a totally uncharged state. To ensure maximum battery performance, a new battery (or battery that has not been used for several months) should be charged for at least 14 hours before use. When charging the battery for the first time, the device may indicate that charging is complete after just 10 or 15 minutes. This is a normal with rechargeable batteries. New batteries are hard for the device to charge; they have never been fully charged and not "broken in".To be completely and deeply charged, a new battery will require several full charge/discharge cycles in order to achieve its optimum performance. A new battery, or battery that has not been used for several months, may cause a premature fully charged indication as well. Ignore this indication and let the battery charge for several hours. Don't worry, it's perfectly normal.