RULE NO. 1: Never Leave Batteries Unattended While Charging
While the charger does its thing, you can work on your car, vacuum, watch TV, anything — but don’t leave the room for the duration of charging, and for heck’s sake, don’t leave the house. 99.999% of the time, batteries charge without a hitch. But if you’re in the 0.0001%, being by the charger is what will prevent damage to your RC gear and other property.
RULE NO. 2: Use the Right Charger
NEVER USE A NIMH CHARGER WITH LIPO BATTERIES. Yep, all caps, because LiPo batteries tend to catch on fire if you try it. So don’t. You MUST use a LiPo charger (or a LiPo charge mode, if you have a multi-mode charger) when charging LiPo batteries.
RULE NO. 3: Use the Right Connectors
If your charger and batteries don’t have the same type of connector, purchase the appropriate adapter, or install the correct connector (or have one installed for you). Never jerry-rig connections with exposed wires or clips, as these may cause a short circuit that could damage your charger, battery, or even start a fire.
For extra safety, a flame-retardant charging bag (such as this one from MaxAmps) is a good idea.
LiPo Balancing: what It Is And Why You Should Do It
When purchasing a LiPo charger, make certain it has the ability to balance the cells in the pack as it charges. When a pack is “balanced,” it means the cells have the same voltage. For example, a 2-cell, 7.4 volt pack is balanced if both cells have 3.7 volts. If you don’t balance the cells, their voltages may drift after a few charge/discharge cycles. Why does this matter? Because LiPo cells don’t tolerate being over-discharged well. And while your speed control’s low-voltage detection system (see “Caring For Your Batteries”) will prevent the pack’s total voltage from dropping past a certain point (let’s say its 3.3 volts per cell, or 6.6 volts for a 2-cell pack), the speed control only “sees” the total voltage of the battery, not the voltage of each individual cell. So, if the pack is unbalanced, that 6.6 volts might not represent 3.3 volts per cell; you might actual have one cell at 3.6 volts, and another at 3 volts—that cell will be over-discharged, and now your pack is compromised or even ruined. Balancing ensures the cells always have equal voltage. Happily, balancing is easy to do; in most cases, all you have to do is make certain the pack’s balance plug is plugged into the charger.
Depending on your charger, there may be a built-in balance plug port, or an external “balance board.”
The small white connector you’ll find on most LiPo packs is the “balance plug.” It’s wired so the charger can read each cell’s voltage individually and charge accordingly.