18650 Low to high amps

[pomkon]

There are specific rated amps labelled on 18650 batteries. from 5A to 30A (continuous??) How can they vary so much? When is considered high, low and normal? Which devices need what? 

 

What if u put a 30a 18650 into a 3A device? The battery will adjust itself? but still drain quicker?

 

what dont typical AA has amps specified? 

[Tabs]

They vary a lot because although most lithium cells are just considered "lithium ion" or "lithium polymer", the actual composition of the battery varies a LOT. Cheap cells might only manage a low continuous current, while expensive cells can handle more.

 

If you put a cell capable of 30A in a device that draws 3A then the battery will output 3A. The rating is an estimate of the *maximum* it can output, nothing more. As long as the battery is capable of at least the current draw that the device requires, it'll work. However, high current handling cells tend to be more expensive, so you have to decide whether paying more for a higher current cell is worth it for whatever device you're using.

 

Low current devices like LEDs can get by with basically any cell. High current devices like RC model aircraft etc need much higher current handling and so they need the better cells.

 

AA don't have their current specified because they work differently. Lithium cells can output the same current right down to their termination voltage, but AA cells output lower and lower current as their charge drops. It just isn't a useful metric for those kinds of cell.

[Tabs]

Just as an aside, if you look into this a bit more you'll encounter something called a C rating for lithium cells. The C rating is the amperage a cell can discharge, multiplied by its capacity. This is an extremely important figure to consider, because it shows how "capable" the cell itself is. If a 1000mAh cell and a 2500mAh cell are both rated for 10A, it means that the 2500mAh cell is only capable of 40% of the current handling for the same relative amount of capacity (2500/1000). In this example, the 1000mAh cell would be 10C (10A/1Ah) and the 2500mAh cell would be 4C (10A/2.5Ah).