A "smart" charger is a designed to quickly and safely charge your airsoft batteries while preventing the issues that can normally come along with a standard wall charger. The charger that may be included with your airsoft gun right out of the box is not very high quality, and has potential to ruin your batteries while also taking quite a long time to charge. Your charger isn't worth messing with if it looks like this:
The biggest downside of "dumb" chargers is that they have a high chance of ruining your batteries. These chargers charge batteries at a constant rate, even if they're completely full. This method can be very harmful for the cells, which is why you'll notice your batteries getting warm or even hot when charging on a "dumb" charger. Since these chargers have no way of telling you when your battery is fully charged, it's a guessing game as to when your battery is done. Guess it wrong and your battery is either undercharged, leaving you vulnerable out on the field, or may be overcharged and completely broken.
These "dumb" chargers also can take quite a while to charge. It will take anywhere from 4 to 8 hours to charge a standard mini battery on a dumb charger, depending on the amperage of the charger, capacity of the battery, and how much charge the battery pack still had before charging. There's no surefire method to knowing just how long your battery will take to charge with one of these chargers, so it's just a matter of hoping for the best.
A smart charger fixes both of these issues very handily. There's an indicator light that will tell you exactly when your battery is completely charged, which entirely prevents overcharging. Should you forget your battery and leave it plugged in, these chargers have a special "trickle" charging function that automatically turns on when the battery is fully charged and keeps the cells active and at their maximum capacity without overcharging. Additionally, due to these safeguards, the smart charger is able to charge at up to 1.8 amps, enough to charge a 1800mAh battery in just one hour.
Whether it's saving time or protecting your airsoft battery packs, a smart charger such as the Tenergy Smart Charger is a great investment for your airsoft kit.