Seems to be C-rate[1], a unit specifically for battery discharge rate. Funny enough, the wiki article does mention disambiguation between it and Coulombs.
> Charge and discharge rates are often denoted as C or C-rate, which is a measure of the rate at which a battery is charged or discharged relative to its capacity. As such the C-rate is defined as the charge or discharge current divided by the battery's capacity to store an electrical charge. While rarely stated explicitly, the unit of the C-rate is [h^-1], equivalent to stating the battery's capacity to store an electrical charge in unit hour times current in the same unit as the charge or discharge current.
Generally given a battery chemistry and manufacturing technology, the charge rates and discharge rates are given in units of "C" which means it allows 1A charge/discharge per Ah capacity of the battery. For instance, the lipoly batteries I got for my combat robot last year were 20C discharge, and 1C charge, and had a capacity of 1800mAh. This means I can discharge at 36A, charge at 1.8A. While true, the charge rate doesn't scale with discharge rates directly, for a given chemistry, it does.
In battery terminology, and this paper, charge/discharge rate is referred to as "C". Charging or discharging at 1C means a battery would be fully charged/discharged in 1 hour. A 100 Wh cell discharging at 1C would produce 100 W. Likewise, at 3C it would take 20 minutes and produce 300 W. At C/3, it would take 3 hours.
That technique is called Coulomb counting and is the standard way of giving a precise battery charge percentage for lithium based batteries. The battery capacity estimate is improved over time based on the previous observed amounts of energy to enter or leave the battery.
C is the rate that the battery can be discharged (or charged). A rate of 17C suggests the battery can be fully discharged in 1/17 hours. The actual current/power this produces is dependent on the battery itself.
"A C-rate of 1C is also known as a one-hour discharge; 0.5C or C/2 is a two-hour discharge and 0.2C or C/5 is a 5-hour discharge. Some high-performance batteries can be charged and discharged above 1C with moderate stress."
They use coulomb counting, along with an estimate of how much safely-usable energy is left in the battery.
That estimate is usually accurate, but it can drift a bit over time if you never fully recharge or discharge the battery. Also, when the battery gets old it starts having trouble delivering full current when mostly discharged, which is why you'll sometimes see shutdowns at 5-15% remaining.
I looked up this "C rating". 0.6C means that the battery will be completely discharged in 1/0.6 hours.
Well, more precisely, it means that it is producing 0.6 * X amps where X is the battery's capacity in amp-hours. Since discharging a battery at a rate of 0.6 * X amps usually produces less heat than discharging it at X amps, the battery is (usually) slightly more efficient, which means it will usually continue to provide power for slightly more than 0.6 hours.
Hopefully, the person I am replying to will correct me if I have made an error here.
I wonder what "rates 10 times faster than lithium-ion" are meant to be? 1C (full charge/discharge in 1 hour) is somewhat common in li-ion. So, 10C then? (full charge/discharge in 6 minutes)
I think you got it backwards, "C" is for capacity (useful since (dis)charge current obviously scales with capacity, ceterus paribus) and a 2C discharge rate is twice the current of a 1C rate.
You also need to be careful in your calculations. Battery discharge rates are given in Amps (or C multiples) not Watts because over a cycle, cell voltage will naturally drop. Discharging at 5 Watts puts more strain on an empty than a full cell since the first requires higher current to compensate for the lower voltage. Amps reflect the "demand" better.
Your summary is still correct though, there is more margin for degradation in a laptop battery and space for decoupling.
It's the energy capacity of the battery divided by the power of the battery; i.e. if you discharge the battery at maximum power, how long does the battery last?
> When if it was just rated in Wh we'd actually know.
No.
The capacity literally changes depending on how fast you draw.
This is especially a problem on lead acids, so they often have couple "n-hour rate capacity" figures to make estimates for your particular use cases. It's less of a problem for li-ion, where C-rates(not coulomb but alphabet cee) is used to plan for cell counts, runtime, current limits and required wire thickness(because wire thickness depends on current, yet again, not total energy through it). It's a non-issue for dry cells because it's among equipment designer's responsibilities to account for.
And that has little to do with Wh vs mAh. It'll be easier to guesstimate more precisely from mAh using experiences and implications, if anything.
[1] https://en.wikipedia.org/wiki/Battery_(electricity)#C_rate
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