I am making some experiment on the 18650 battery, I learnt that their charging voltage is 4.2v while nominal voltage is 3.7v. I made a 2ways parallel connect of 3 serial connection just like the laptop battery pack, on the laptop 11.1v is written which is 3 x 3.7v but I charge the battery with a 12.5v charger which is still with the charging range of the cell 4.20v * 3=12.6 and the battery is now charge to 12.3v and started getting warm so I disconnected it even despite that its not yet up charge to my charger range. But the problem is that I dont know if 12.3v would damage the laptop if I connect to the battery port with the circuit since they wrote 11.1v, and i would like to know what that nominal voltage mean and I would to know maybe if I increase the battery cells from 6 to maybe 9 or 12 in other to increase the amp/h would it damage my battery. If would be very greatly for your help
Electrical – Can 12v destroy a laptop instead of 11.1v
cell-batterylaptop
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Cells in devices that you do not wish to be a flaming ruin MUST have protection.
Having protection circuits does not guarantee it will not happen.
Cells without protection are intended for use by either manufacturers or experts or enthusiasts who add their own or for suckers.
Whole device protection and cell protection are complementary and serve overlapping but different roles.
4,000 mAh 18650 LiIon batteries are ~~~= 99.9% +0.1% - 0.0% sure to be rubbish.
ie not just < 4000 mAh but << 4000 mAh and low quality.
The people who bogus label cells
almost never feel an obligation to use the best cells they can and
almost always decide to add injury to insult by using junk as well as lying.
Real world experience shows that the value of 'almost' is very high in both cases.
Higher capacity cells can usually be fitted OK.
MUCH higher capacity will lead to long CC tails and overcharge but not an issue here as mAh_new is < to << 4000 mAh.
ADDED:
Notice that in this ad and all their other ads they ALWAYS show non-brand-label views of the battery.
However, you may find that the racing stripes and general colour scheme a good match for the well known "Ultrafire" brand batteries. This may in fact be a real brand and these may be real examples of it BUT you can buy empty shrink wrappers to apply to the battery of your choice with this (or other) branding on it , so caveat emptor. Better nullius emptor I'd hazard.
These ones are a stunning 6800 mAh - a steal at the price. Available here
You'll find others similarly arrayed here and
here - 3000 mAh and 4000 mAh and
6800 mAh !!!!!!!!!!!!!!!! {again}
and unspecified but with GENUINE CREE 2000 lumen {so 20+ Watt} flashlight for $9.27 and
only 4000 mAh and
that's better - 4200 mAh
and .............
Flee!
At 3.3~3.4V a 3.7V Lithium ion cell has practically no capacity left, and is past the 'knee' where increased current causes a large voltage drop. At this low charge state, small differences in capacity between cells also become significant, and some cells may drop their voltage before others.
In the graph below showing discharge of a typical modern 18650 cell at various currents, I have added a red dot showing where it reached 3.4V at 0.2C. At this low current the curve should be similar to open circuit - a bit lower but with a similar rapid drop. If you extrapolate and line up the discharge curves to meet at 0V then you can estimate what the voltage would be at higher current.
But what does this mean for determining "best" 18650 cells to replace the ones in your laptop? The laptop probably refused to start because the voltage under load went below the minimum it accepts. You don't know what that cut off voltage is, but you do know that the battery had practically no charge left, so it was past the 'knee' where voltage drops rapidly. So long as your replacement cells have a similar discharge characteristic they should be OK, and the exact cutoff voltage probably isn't that important.
Best Answer
The voltage on the battery pack, really any rechargeable pack of any chemistry, is a nominal voltage. With Lipo cells this is typically the 90% charged voltage. The fully charged voltage will quickly drop over time or under high load due to its internal ESR and voltage curve (check the datasheet). A Lipo will then stay at its nominal voltage for most of the charge before quickly dropping when discharged. A 1.5V alkaline battery in comparison has a fully charged voltage of 1.6x V to nominally discharged at 1.1V, and fully discharged are 0.6V. 1.0 to 0.6 volts will be super dead and need something like a Joule thief to get out. A fully charged Lipo is much higher than its stated 3.6, 3.7 or 3.8 volt markings.
That said, there is no way to know how tolerant your random laptop is to the slightly higher voltage. When the laptop fully charges the battery, it is using a dedicated Lipo charging system, a battery monitor or gas gauge, and knows when to cut it off. You do not seem to have done the same.
That said again though, 12v isn't much higher than 11.1V. 9% higher. It will likely be fine. The laptop would use a higher voltage to initiate charging anyway. But use it at your own risk.