Rechargeable Battery Fundamentals - Capacity/Charging

Rechargeable Battery Fundamentals, what to look for and how do they work?Rechargeable batteries are the smartest way to power your digital camera, both in terms of battery life and cost. There are two types available: Nickel Cadmium (NiCd) and Nickel Metal Hydride (NiMH). Before you purchase ANY type of rechargeable battery you MUST READ below to AVOID DISASTER.Dont be tempted to go for the cheaper NiCd batteries. Not only are they extremely bad for the environment but they suffer from a well-known problem called the memory effect. The memory effect is the term given to the tendency of NiCd batteries to deliver much reduced power output if they are incorrectly charged and discharged over time. If a NiCd cell is charged while it still has capacity left in it, the battery will forget that it had that capacity and will not be able to use it. All NiCd batteries should be fully discharged before they are charged again to avoid the memory effect. NiMH batteries are the best option for rechargeable batteries, and to be honest they should be the only type of rechargeable battery you buy. They deliver better power output, dont suffer from the memory effect, and are compatible with the majority of chargers. When choosing a NiMH battery check for these things: Cell capacity: All NiMH batteries have a capacity rated in milliamp hours. This figure will typically be found on the side or back of the battery with milliamp hours abbreviated to mAh or mAH. A milliamp hour is the theoretical amount of milliamps (mA) the battery can deliver for one hour. A 2200mAh battery will be able to deliver 2200mA for one hour, or 1100mA for two hours, 550mA for four hours and so on. It must be taken into consideration though that not all cells are created equal, this is due to a huge variance in design and manufacture. Aside from that the stated capacity is rarely the capacity available as some power is lost through heat and dissipation. The battery should be pretty close to its rating though. Basically what you are looking for is the highest capacity possible, at the moment this is around 2700mAh although more commonly 2500mAh or 2300mAh. Anything below this should be avoided. Charging: A charger feeds an electric current rated in milliamps (mA) to a cell for a certain amount of time. This could be a large amount of current over a small amount of time or a small amount of current over a long period of time. In theory the first option is better for the end user as the battery will be charged more quickly. However in practice this isnt the case, putting a lot of current into a cell over a short amount of time leads to an increase in temperature which shortens the batteries life and its power output. It is for this reason that quick chargers should be avoided. Thankfully it is easy to work out roughly how long a battery should take to be fully charged in any charger provided you know the batteries capacity in mAh and the charging current in mA. The batteries capacity should be easy enough to find printed on the battery itself, the charging current should be found on the back of the charger. All NiMH batteries need roughly 1.5 times the amount of energy put in as they are going to get out. So a 2200mAh battery will need 3300mA energy put in to be fully charged. To work out how long a battery will take to charge you simply multiply the cells capacity by 1.5 as explained, and than divide this number by the charging current in mA. So for the previous example it would take the 2200mAh battery 16.5 hours to be fully charged if using a 200mA charging current (3300mAh 200mA = 16.5). This can be taken as a general guide; in practice a charger will monitor certain characteristics within a battery to tell when it has reached capacity. The last thing to be aware of is that unlike Alkalines, NiCd and NiMH rechargeable batteries will not hold their charge for an extended period of time. Alkaline batteries are typically still usable more than five years from purchase whereas a typical rechargeable may go flat within months if not used.