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Ubuntu tells me in the menu bar that my battery percentage is 86%:

enter image description here

While tlp-stat says it should be 95.9%

sunqingyao@sunqingyao-MacBookAir:~$ sudo tlp-stat -b
--- TLP 1.0 --------------------------------------------

+++ Battery Status
/sys/class/power_supply/BAT0/manufacturer                   = DP
/sys/class/power_supply/BAT0/model_name                     = bq20z451
/sys/class/power_supply/BAT0/cycle_count                    =    154
/sys/class/power_supply/BAT0/charge_full_design             =   7150 [mAh]
/sys/class/power_supply/BAT0/charge_full                    =   6435 [mAh]
/sys/class/power_supply/BAT0/charge_now                     =   6169 [mAh]
/sys/class/power_supply/BAT0/current_now                    =   1471 [mA]
/sys/class/power_supply/BAT0/status                         = Charging

Charge                                                      =   95.9 [%]
Capacity                                                    =   90.0 [%]

Which one is correct?

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    I would guess tlp-stat is the more accurate. According to what you posted, the battery is currently being charged so tlp-stat is updating in more-or-less real time. Ubuntu is probably looking at a sensor somewhere and likely updates less frequently. It's also possible that each monitoring method uses different math to arrive at the percent of charge. Again, tlp-stat probably being the more accurate.
    – jones0610
    Jul 12, 2017 at 4:35
  • @jones0610 Thanks for your responding! I'm going to charge the battery to full, and then track both battery indicators over several hours.
    – nalzok
    Jul 12, 2017 at 4:40

1 Answer 1

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24

I'd say both are:

since it says Capacity 90% and Charge 95.9% I would guess the menu bar shows you

Charge * Capacity = RealCharge
95.9%  * 90%      = 86.3%

Capacity is the maximum capacity that your battery is able to charge to. This can and will decrease with time for technical reasons, and your battery will charge and discharge faster as it gets older because of this decreased capacity. This value might differ slightly while charging but should more or less only decrease with time.

Charge is the percentage of how charged your battery is compared with its maximum capacity.

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    Does this mean that when fully charged the menu bar would display a 90% charge? That would seem like a choice prone to worry users (although it would be more informative)
    – Aaron
    Jul 12, 2017 at 13:00
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    yeah it seems so .. I didn't say that it's a good choice of the makers of this menu bar .. I only guessed as I said that this is where the number comes from
    – derHugo
    Jul 12, 2017 at 14:23
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    @Aaron: To be fair, worrying them is what you want, rather than hiding the fact that their battery may now only give them like 20 minutes' of use ("huh? how is that 100%"?) but at the same time I've never seen this behaviour elsewhere
    – Lightness Races in Orbit
    Jul 12, 2017 at 17:23
  • @Aaron yes, but that reflects the fact that it's only holding 90% as much charge as it did when it said 100%. It's bucking the convention, but in a real way it's more accurate.
    – hobbs
    Jul 12, 2017 at 19:12

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