When fired point blank, plastic BBs can hurt as much as rubber bullets, however most people engaging in military simulations with airsoft guns wear thick military garb. Additionally, precautions are taken to protect the neck, face, and eyes. Many people chose to wear a balaclava around their face and neck and cobalt ontario copyright ANSI approved eye protect is a must. The only place that plastic BBs can really cause damage is to your eyes.
The battery will over-charge if left attached to the charger. The battery stops charging automatically when full lithium facts so it will not over charge. If the battery is left on charge too long it is possible that heat will damage the battery.
The lithium-ion battery is light years ahead of the earlier batteries and considerably better than the Nickel-cadmium (Ni-Cd) or the nickel-metal hydride (Ni-MH) batteries which are still being used. These batteries are less expensive but the Li-ion batteries are far superior in three ways.
Avoid using replacement that has been on lithium bettery stock for a while. During storage the battery can lose much of its capacity through internal resistance, which damages it and lowers the maximum capacity.
You have more power to perform work better and faster such as drilling and screwing than the smaller model. Once I used the 18v model I found that I prefer to use it more often because it gives me more power to complete the same task with less effort. At the end of the day it is better and faster, productivity counts.
The bottom line, be gentle to your lithium-ion batteries. If you excessively charge the battery, with high voltages, and heavy load conditions, it will shorten your battery's life. It's best to charge at a slower rate.