Battery(61Wh) discharge curve

[Charlie_6]

@Adrian_Joachim

But hey they claim 20% capacity loss after 1000 cycles at full capacity so I am curious how it actually turns out.

Too little information.
What’s the temperature during charging discharging? A higher temperature means much lower cycle life.
What’s the discharge cut-off voltage? A lower cut-off voltage means deeper discharge and higher degradation.
What’s the charge cut-off current? During constant-voltage phase, the charging current goes lower as the battery % increases, when the current is below a certain value the current is cut and the charging is finished, continue charging nonstop will overcharge the battery even the limited charging voltage is never exceeded. Most classic 18650/21700 battery manufacture specify a 0.03C cut-off current.
What’s the charging C-rate? A higher rate means lower cycle life, batteries rated 1C charging often charge at 0.2C during cycle life testing, in this case if you always charge it at 1C it’s cycle life will be significantly lower than it’s specification.
What’s the discharging C-rate? same as above, batteries rated 2C or even 5C might still discharge at 0.5C during cycle life testing.
Here’s an example, note that the battery cell is capable of doing 2C discharge but cycle life test is done at 1.0C
No specification about calendar life, battery degrades over time, the higher the % the worse the degradation, the best storage % is 30~40%. Although 30%~40% is better than store at 100%, the battery will still degrade. To get the max cycle life one would charge/discharge non-stop to minimize calender life loss, which is the opposite of actual usage.

@anon81945988

The battery is the 55W: 26 month old and has just done it’s 101 cycle, however the wear is at least 12% not 2% as I would have hoped.

Practically, battery almost never get to the rated cycle life on the datasheet.

1. Prolonged storage. Longer time is spent per 100 cycle in actual use regardless of %, compared to test condition. (worse)
2. Elevated temperature. No battery cooling, heat is conducted via the metal casing, while the CPU has dedicated cooling but still conduct heat to the surrounding parts, meaining the battery temperature sits between CPU and ambient. To make matters worse. There’s no temperature reading on the AMD7840U w/61Wh battery (worse)

@DHowett

I haven’t seen any indication of battery temperature reporting on my AMD Frameworks Laptop.

And the CPU runs straight to the wall (100C) before underclocking. And there’s no official way to enable S3 and disable S0ix sleep. In modern standby the CPU won’t underclock if M$ is abusing your laptop’s computational power till it’s last leg(I witnessed much higher power comsumption on modren standby compared to idling on desktop or browsing websites or documents). Either use Linux(modren standby consumes 2.5 to 25 times of wattage compared to s2idle), or use some sort of hacks such as UMAF to emable S3, otherwise when sleeping(more like pretending to be asleep) in enclosed space such as inside you backpack, the CPU will constant temperature operation while conducting heat to other components such as the battery. Since there’s no indication of battery temperature the battery will continue heating up to 100C before death instead of shutting down the system upon overheating. If there’s no official fix, an onboard fire aviation accident caused by modern standby is going to happen sooner or later.

3. Higher charge/discharge rate. The battery discharges at 3915mA(1C) max and during charging and if the power supply is sufficient, 3915mA to 40% then 2740mA(0.7C) when above 40%. If the cycle test is done on 0.2C or 0.5C, the actual cycle life will be lower. (worse)

4. Lowered limited charging voltage. If the user use 80% limit at 99% of the time, the cycle life will be higher compared to testing. (better)

Conclusion: since there are more factors that lowers the actual cycle life compared to those extend it. The battery will more likely to degrade faster

@Adrian_Joachim

Allowing a lower charge limit is probably a massively bigger factor than the hysteresis thing, a few small charges and discharges are about equivalent to one bigger one wear wise, but doing the same dance at 80% vs at 100 is going to produce a lot less wear.

About the HP Omen battery degradation, thing.

1. It does not undervolt, the limited charging voltage is 4.4V/cell. Many older computer runs on 18650 batteries that has a limited charging voltage of 4.2V/cell but the laptop manufactures program the BMS to limit the charging voltage to 4.1V/cell.
2. It does not have a hysteresis loop, mentioned earlier.
3. It did not have user-configurable charge %, before a later BIOS update.

I found that most laptops with swappable battery pack with cylinder cells, the battery pack degrades much slower compared to modern laptops or smartphone where the cells are in pouch format, even if most of the former don’t have charge limit adjustment. which means that 1 & 2 can be as effective as 3.