There are three general types of rechargeable batteries available for otoscopes including Nickel Cadmium (NiCad), Nickel Metal Hydride (NiMH), and Lithium Ion (LI-ON). Appreciating how these battery technologies differ from one another should help in making an informed otoscope purchase decision in the future.
Of the three battery technologies, NiCad batteries are prone to what is referred to as a memory effect. Memory effect refers to a battery’s inability to remember how much reserve capacity it has left prior to recharging. If an otoscope powered by a NiCad battery has used up only 60% of its capacity when it gets recharged, the battery “forgets” about the 40% reserve capacity; while the battery will successfully recharge, it will now assume a 60% capacity rather than the original 100%. To avoid this, make sure the full reserve of the otoscope battery is used up prior to recharging.
Capacity refers to the amount of energy a rechargeable battery holds. Both NiMH and LI-ON batteries maintain higher capacities than NiCad batteries with LI-ON batteries holding more than NiMH. Batteries with higher capacities will obviously run longer but without necessarily adding additional bulk or weight to the battery. For example, a full-size otoscope handle powered by a LI-ON rechargeable battery not only holds more energy, it also weighs about half as much as a NiCad full-size handle.
Discharge rate refers to how quickly a battery expends its capacity. LI-ON batteries have much slower discharge rates than NiCad or NiMH batteries and will, therefore, retain their charge about twice as long. Furthermore, LI-ON batteries retain most of their charge even after months of non-use. In contrast, NiMH and NiCad batteries can lose anywhere from 1% to 5% of their charge per day respectively even if the battery isn’t being used.
Of course, you don’t get something for nothing. While LI-ON batteries provide many advantages, they cost more. On average, a rechargeable LI-ON otoscope handle will run about $180 more than a NiCad handle with the LI-ON replacement battery about $100 more than a NiCad replacement battery.