Certain electronic products require a special format battery charger, which is usually provided by the manufacturer. The average battery charger has a capacity of either four or six batteries. Ideally, you should have at least an extra pair of charged batteries on hand at all times, so make sure your charger can handle the load. Avoid battery chargers that do not have an "end of charge control" too much output current can ruin a battery in just a few hours.
Never leave an unregulated or so called "automatic" charger connected to your battery overnight, unless it shuts off completely. One feature worth spending extra money on is a charger control. Timer Module An expensive battery charger has an intelligent microprocessor that switches the charger off when the batteries are fully charged. It can also recognize how much charge is originally in the batteries and only add whatever's needed. Cheaper chargers, on the other hand, charge batteries for a fixed length of time, which can overcharge the battery and shorten its life. A simple LED is typically used to indicate when the charge cycle is complete.
The battery charger size you choose depends on the charging current required to restore the battery to full charge. Battery capacity is expressed in Amp Hours and is a figure of merit used to work out battery life between charges. You can connect a number of batteries in a series or parallel combination when recharging. Remember that the battery charger rate is limited to a maximum charging current depending on the model you select and this in-turn, limits the number of batteries you can recharge at any one time.