Follow-up entries are always fun.
About a year ago I wrote about how recalibrating my laptop’s battery significantly increased its performance. Well I’d like to report by religiously recalibrating every three months, the two year old battery has a capacity of 83.7%, down only 1.6% from a year ago. Yay.
One important thing I learned was inducing a quick discharge hurts the capacity. For one recalibration, I maxed out the CPUs and disk I/O, kept a CD spinning, and saturated the wireless network interface. While it proved to be a quick recalibration session (discharged to ~3% in well under an hour), it dropped the battery capacity to 60-something percent. Eeep. So yes, when recalibrating, it’s best to using the laptop as normal, and not do anything crazy.
But wait, there’s more!
The methods GNOME Power Manager used to calculate a battery’s current and design charges, and thus capacity, has changed in the last year.
Calculating current charge has gone from
current charge in Wh=(remaining capacity in mAh/1000)(present voltage in mV/1000)
to
current charge in Wh=(remaining capacity in mAh/1000)(design voltage in mV/1000)
And design charge from
design charge in Wh=(design capacity in mAh/1000)(present voltage in mV/1000)
to
design charge in Wh=(design capacity in mAh/1000)(design voltage in mV/1000)
Since present voltage was swapped for design voltage, both methods yield the same capacity percentage, so it’s not as if the change caused a misleading result concerning the steady capacity over time. Consider the following:
Metrics of the battery one year ago
/proc/acpi/battery/BAT0/info
present: yes
design capacity: 6000 mAh
last full capacity: 5120 mAh
battery technology: rechargeable
design voltage: 14800 mV
design capacity warning: 262 mAh
design capacity low: 158 mAh
capacity granularity 1: 10 mAh
capacity granularity 2: 25 mAh
model number: Primary
serial number:
battery type: LION
OEM info: Hewlett-Packard
/proc/acpi/battery/BAT0/state
present: yes
capacity state: ok
charging state: charged
present rate: unknown
remaining capacity: 5120 mAh
present voltage: 12410 mV
Old method of calculation:
Current charge = 63.5392 = (5120/1000)(12410/1000)
Design charge = 74.46 = (6000/1000)(12410/1000)
Capacity percentage = 85.33 = (63.5392/74.46)(100)
85.33%
New method of calculation:
Current charge = 75.776 = (5120/1000)(14800/1000)
Design charge = 88.8 = (6000/1000)(14800/1000)
Capacity percentage = 85.33 = (75.776/88.8)(100)
85.33%
Metrics of the battery now
/proc/acpi/battery/BAT0/info
present: yes
design capacity: 6000 mAh
last full capacity: 5024 mAh
battery technology: rechargeable
design voltage: 14800 mV
design capacity warning: 257 mAh
design capacity low: 155 mAh
capacity granularity 1: 10 mAh
capacity granularity 2: 25 mAh
model number: Primary
serial number:
battery type: LION
OEM info: Hewlett-Packard
/proc/acpi/battery/BAT0/state
present: yes
capacity state: ok
charging state: charged
present rate: unknown
remaining capacity: 5024 mAh
present voltage: 12356 mV
Old method of calculation:
Current charge = 62.076544 = (5024/1000)(12356/1000)
Design charge = 74.136 = (6000/1000)(12356/1000)
Capacity percentage = 83.73 = (62.076544/74.136)(100)
83.73%
New method of calculation:
Current charge = 74.3552 = (5024/1000)(14800/1000)
Design charge = 88.8 = (6000/1000/)(14800/1000)
Capacity percentage = 83.73 = (74.3552/88.8)(100)
83.73%
Huzzah.
