They look the same but have major differences.
The numbers "1800" or "2800" printed on NiMH (nickel metal hydride) rechargeable batteries typically identify their capacity in milliamps, often referred to as "mA" or "mAh." These amounts convert to 1.8 or 2.8 amps. Although both these types of NiMH rechargeable batteries basically work the same way, they have several important differences regarding charge/depletion times and total lifespan.
Charging
The 2,800-milliamp NiMH battery will take longer to fully charge than the 1,800-milliamp version. For example, suppose a certain battery charger charges batteries at 110 milliamps per hour. It will take roughly 25 hours to completely charge the 2,800-milliamp NiMH battery or 16 hours to charge the battery with a capacity of 1,800 mA. However, it's safe to charge a 2,800-mA rechargeable battery somewhat faster (using more amperage), although many chargers don't provide this option.
Depletion
The higher-capacity battery will take longer to deplete than the 1,800-mA type. As an example, a model TRC-92 portable CB radio draws about 24 milliamps in receiving mode, according to its manual. If it operated on the power of a 2,800-mA NiMH battery, it could run for up to 117 hours. On the other hand, an 1,800-milliamp rechargeable battery would power it for a maximum of 75 hours. However, REI indicates that some batteries with lower capacities don't discharge as much in storage. The newer the rechargeable batteries, the longer they will supply adequate power.
Cycles
To gain higher milliamp capacities, rechargeable battery manufacturers alter NiMH batteries in ways that decrease the maximum number of charge cycles, according to REI. BatteryStuff indicates that batteries in the 1,800-milliamp range provide a maximum of 1,000 cycles when charged slowly (with a low-amperage charger). Using the same method, rechargeable 2,200-mA batteries charge around 700 times and 2,500-mA batteries about 500 times. This trend suggests that 2,800-milliamp NiMH batteries would achieve somewhat fewer cycles.
Lifespan
The factors regarding charge cycles and depletion times both create differences in the overall lifespan of NiMH batteries. If the 2,800-mA battery were to power the TRC-92 CB radio for 117 hours during each of 400 charge and discharge cycles, its lifespan would add up to 46,800 hours under ideal conditions. On the other hand, the 1,800-mA battery would run it for 75 hours during 1,000 cycles, for a maximum of 75,000 hours. Overall, the lower-capacity rechargeable battery offers a longer lifespan but requires more charging sessions.
Tags: rechargeable battery, 800-milliamp NiMH, NiMH batteries, NiMH battery, rechargeable batteries
