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This question is exact oposite of this question

Laptop specs lenovo G470

Battery specs

  1. Original ( which came with the original laptop i.e laptop in quetion)-

  • Power rating- 11.1V-48Wh (P=VI , so i=4.324)

  • Model number- L09M6Y02

  1. Replacement- (also original but from a different laptop)

  • Power rating- 10.8V-48Wh (P=VI , so i=4.444..)

  • Model number- L11L6Y01(3INR19/65-2)

Note-this battery has been sitting for almost 2 years without being used

Charger 20V-4.5A (for both)

So, is it safe to replace original 10.8v with the replacement battery?

Chemist
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1 Answers1

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They're actually the same.

Lithium-ion and lithium-polymer cells have nominal voltages in the range of 3.6-3.8V. Their actual voltage fluctuates though, it can be slightly higher when the cell is charged. Your battery contains three such cells nominally rated 3.7V each, 11.1V in total because they're connected in series. The replacement battery has cells with nominal voltage of 3.6V, totaling 10.8V.

But as I said it's normal that voltage changes slightly throughout charge-discharge cycles and laptop's circuitry is prepared to handle it. It's actually using this relatively high voltage to produce a number of lower voltages, such as 5V, 3.3V and 1.2V. DC-DC converters responsible for delivering these have feedback signals which are compared to a common reference voltage and independent from input voltage.

I suppose the laptop circuitry would be good with anything between 10-12V and could probably go even lower safely.

The charger voltage is irrelevant, there's another step-down converter which produces voltages required to charge the battery and power the rest of the laptop while it's plugged in.

gronostaj
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  • hey, i opened the battery case, i found 6 cells, in both the batteries also when i connected the replacement battery voltage was 8.1. it says charging at a rate 2.1w even after one hour amount of power in battery is still 0.4Wh, should i presume its dead? – Chemist Jun 24 '20 at 07:29
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    It's probably a [2P3S configuration](https://us.reddit.com/r/AskElectronics/wiki/batteries#wiki_arrangement), very common in laptop batteries. 8.1V is suspiciously low, that would be 2.7V per cell (maybe one cell or pair is dead?). 0.4Wh suggests that it wasn't consistently charging at 2.1W because 2.1W * 1h = 2.1Wh. The charging circuitry may have detected the problem and stopped charging for safety. – gronostaj Jun 24 '20 at 08:06
  • now the voltage is 11.2v and charging rate is 26.8w. – Chemist Jun 24 '20 at 08:08
  • its 1.35 per cell before, because there are 6 cells,now its 11.3v so 1.8 per cell – Chemist Jun 24 '20 at 08:13
  • so as the voltage is increasing charging rate also increasing , now the energy in battery 4.9Wh with voltage 11.3 and rate 27.3w – Chemist Jun 24 '20 at 08:14
  • earlier 8.1v volt because maybe battery was in deep discharge due to non usage for almost 2 years – Chemist Jun 24 '20 at 08:17
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    You don't have 6 cells in series, where their voltage would sum up - that would produce over 20 volts once the battery is fully charged. It's a 2P3S setup: cells are connected in pairs in parallel (such pair has double the capacity but the same voltage) and those pairs, about 3.7V each, are connected in series. – gronostaj Jun 24 '20 at 08:18
  • oh yeah, you're right – Chemist Jun 24 '20 at 08:19
  • so are the numbers promising? , now its 11.5v rate 26.7w energy 8.1Wh – Chemist Jun 24 '20 at 08:21
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    That's a reasonable voltage, it looks like it's in the 2nd phase of charging and the circuitry thinks it's safe. You may be able to salvage this one. – gronostaj Jun 24 '20 at 08:40
  • i had to restart my laptop, the charge percentage went 100% directly from 36% now voltage is 10.9v :(, can please tell me what can i do about this?. btw i really appreciate you sharing your knowledge with me thanks a lot – Chemist Jun 24 '20 at 09:17
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    I think one of the cells may be dead. Manually replacing it isn't viable, so I'd recommend replacement of entire battery. – gronostaj Jun 24 '20 at 09:39
  • so is there a way to find out which cell is dead, i have already removed the cell out of the battery case.maybe ill replace it with good cell from the original – Chemist Jun 24 '20 at 09:49
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    You could try measuring voltage drops on pairs, but you have to replace all cells anyway because cells with different wear levels shouldn't be mixed (that's the problem you're trying to fix) and you'd have to spot weld them which is quite a hassle for a one-time job. – gronostaj Jun 24 '20 at 09:54
  • well for now i think 20 mins backup is enough for me to save my work during power outage, cuz ill buy new laptop after 4-5 months – Chemist Jun 24 '20 at 09:58
  • hey , i thinnk cells are not dead – Chemist Jul 05 '20 at 18:14
  • because todat it ran on battery for 2hours and still 50% charge is left ,i think laptop is not able to communicate with the battery, because i cant even see the temperature, and it jumps to 100% if i turn of laptop while battery is charging. What do you think about this – Chemist Jul 05 '20 at 18:20
  • Could be a malfunctioning battery controller. If that's the case, charging this battery is not safe. Or worn out cells and the controller can't make sense of readings. Don't trust the 50% figure, faulty batteries often report high charge and then suddenly drop to near zero. – gronostaj Jul 05 '20 at 20:21