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04-20-2016

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Battery consumption patterns

2019-07-10, 9:25 AM

I acquired a T480 last month which by design operates on two batteries (1 - internal 24Wh; 2 - external 72Wh). One of the first odd behaviours I observed was battery 1 won't charge beyond 80% and only charge battery 2.

 

https://www.reddit.com/r/thinkpad/comments/bxrp04/t480_battery_1_not_charging/

 

As with observation notes put on the reddit post, I then further witnessed battery 1 continues charging only after battery 2 was full. During that period, the laptop only consumed battery 2 while leaving battery 1 as an "emergency reserve fuel tank", leaving me to ponder just how healthy is that. But a few days later the roles were reversed with battery 1 depleted first before transitioning to "reserve tank" battery 2. And as of now, it has swapped over the original sequence with the laptop refusing for weeks to use battery 1 until battery 2 depletion.

 

Lenovo Vantage only offers to define charge threshold parameters, and does not offer control over any sort of battery consumption pattern. So what is the exact logic that the laptop has been programmed with to handle multiple battery consumption?

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45 Posts

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SG

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  • Posts: 45
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Re: Battery consumption patterns

2019-07-18, 16:32 PM
So, there's no documentation that explains this behaviour?
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45 Posts

04-20-2016

SG

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Re: Battery consumption patterns

2019-08-20, 18:34 PM

Today I bought a new battery model 61 (flush slim, 24Whr), after undergoing a gauge reset procedure, I see the laptop swap over to internal battery 1. It does not attempt to use the fully-charge new battery 2.

 

From my observations, it appears the laptop favours the battery with the most cycles (older).

 

  • The internal battery 1 has clocked 19 cycles, so when the model 61++ 72Whrs - with 25 cycles - attaches as battery 2, the laptop will drain battery 2.
  • If the newer slim model 61 battery gets attached - with 3 cycles - then battery 1 (with more cycles) will be selected for use.

Is it me or does the battery selection logic appear counter-intuitive?

 

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45 Posts

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SG

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  • Posts: 45
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Re: Battery consumption patterns

2019-08-23, 7:28 AM
So today I walked into the local Lenovo service centre, and got to chat with a technician about the matter. The official documentation for battery discharge he showed me goes
  • discharge replaceable (external) battery (2) to 5%
  • discharge embedded (internal) battery (1) to 5%
  • alternate discharge of both batteries down to 0%
So the consumption behaviour with the original 61++ (72WHr) battery is following that official pattern.
 
The opposite behaviour with the newer 61 (24WHr) battery (whereby internal battery 1 is drained first) is deviant and unexplainable by the technician. The 61 battery has to date only 4 charge cycles while the internal has already reached 24.
 
Unfortunately I cannot afford to leave my laptop/batteries behind for them to test, as I need it for work.
 
BONUS MATTER
 
Every time I remove the external battery, it takes several re-insertion attempts for the laptop to recognise battery 2 is back online. The most effective means I discovered to "nudge" the laptop is to sleep/wake it, which somewhat reminds it the external battery is back.
 
The technician mention that officially, battery changes should only happen after the entire laptop hardware is shut down and switched off, to prevent the chance of short circuits. Hmmm is that what laptop users really do when they swap multiple batteries in and out?
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45 Posts

04-20-2016

SG

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  • Posts: 45
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Re: Battery consumption patterns

2019-08-28, 14:48 PM

Funny how the technician's advice to "just search the Internet" only resulted in pages after pages of customers complaining about the lousy Lenovo battery consumption policy. With that I happened to dig up an older thread with the discovery of the actual logic - tested and verified with my laptop - 

 

https://forums.lenovo.com/t5/ThinkPad-T400-T500-and-newer-T/T480-battery-discharge-problem-internal-battery-goes-first-at/m-p/4490593/highlight/true#M136210

 

Summary: whichever battery that has the better wear ratio (i.e. Full-charge capacity / Design capacity), not by mere charge cycles, will be used repeatedly until it deteriorates to a level worse than the other battery, of which that other battery will be likewise be used until it gets worse, and on, and on.

 

Bravo, Lenovo, bravo. Trying to push for more customers to collapse their internal batteries?

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