The earliest consumer rechargeable batteries were NiCd rechargeable batteries, based on technology perfected in the 1950s. Devices using these batteries would run for only 1/10th to 1/5th as long as they would on alkalines. Fortunately, when the batteries did run down, they could be recharged. Properly cared for, even these early rechargeable batteries would last for several hundred recharges.
The mid 1990s saw the introduction of NiMH batteries. These had very similar properties to NiCd, but with higher capacity, and more importantly, no super-toxic components. The only drawback of NiMH compared to NiCd was a lower maximum current. High-current applications like cordless power tools and electric powered model aircraft and cars continued to use NiCd batteries for some time.
Voltage is not the only important attribute of a battery. A battery produces a voltage, but the equipment it is powering requires that voltage to be delivered at some current, measured in Amperes.
In this area, NiMH batteries have a big advantage over alkalines, being able to deliver significantly more current. This makes them well suited to high-current devices like digital cameras.
Until recently, most NiMH batteries had a very high self-discharge rate. They would lose capacity even when not in use. A good NiMH battery had a self discharge rate of about 1% per day. The best rechargeable NiMH battery you can buy will not last long if you don’t take good care of it. This primarily means charging it correctly.
With NiMH batteries’ lower tolerance to continued overcharging, so-called smart chargers have become more common. In addition to not overcharging, these chargers charge much faster, typically in one to five hours depending on the charger. The reason there are no dumb fast chargers is that overcharging at these higher rates can result in a lifepo4 battery overheating, popping its seals, and possibly starting a fire. A good fast charger is much better for the battery than blindly slow charging it. However, a bad fast charger, one that doesn’t turn off very soon after charging is completed, can damage batteries too.