Continuous Discharge Rating (CDR)

This is the rating that is used by reputable electronic manufacturers, and the one rating that we can use to compare battery discharge. When accurately rated, it signifies the current that a battery can be safely discharged at a continuous rate without taking damage or reducing its capacity.

Rewraps and Chinese manufactured batteries will often overstate the CDR, or use other ratings instead of it. One good example is the maximum discharge rating (or maximum discharge current), which may even be the only rating on the wrap. It is the maximum current that a battery can supply in short intervals (that are most of the times not mentioned on the rating). This is not a rating that should be taken into account when considering a battery, as it is often times misleading. Always look for the CDR of a battery, and cross-check ratings with online sources.

Capacity

Calculated in mAh (milliampere-hours), the capacity of a battery signifies its running time. One mAh is equal to the charge transferred by a steady current of one milliampere flowing for one hour. While this rating is sometimes overstated on battery wraps, this doesn’t happen as often as it does with discharge ratings.

Going over the ratings of reputable manufacturers, you will notice a pattern: there is always a trade-off between CDR and capacity. There is (still) no 18650 with a CDR over 30 amps. At the same time, no 18650 with a capacity at or over 3000 mAh, will have a CDR over 20 amps. Until further notice, any battery that is not rated according to these two rules can be assumed to be falsely rated.

Try to avoid rewraps, as the batteries that are used for them may change at any given time. With 18650s being so readily available, finding a battery from a reputable manufacturer should always be a priority.