How far can LiIon be discharged?

Hey mate correct me if im wrong but if the battery says 2.8 volt cut of for example you need to reach that voltage to get the advertised mah?

Yes, but depending on chemistry and current you might get very close at higher voltage. The rest of the way down to 2 volt will only be few mAh, but will increase the wear of the battery.

10x m8,

I just watched a Discovery documental movie about telecommunication satellites, they stated that some of those use LiIon batteries( they didnt mentioned what type) : they never charge the LiIon pack over 65% of its potential, and nevel let it go down under 30%: thus the pack coud be recharged over 80k times! I was quite impressed realy

1 Thank

This thread should be a sticky. Maybe a title change, so it doesn’t look like a question.


Thank you for summarizing and providing references for us!

The discrepancy between battery voltage under load (with the flashlight turned on) and the rebound voltage measured after pulling the battery out had always been a nagging issue in the back of my mind. Your explanation helped clear that up.

And caused me to re-think my charging/re-charging practices. In the past, I targeted 3.0V (resting) as being the minimum I’d like to see my battery levels when recharging. However, if the rebound voltage is 3.0V, then the voltage under load might have been somewhere under 2.5V - not good! So, that means I’ll need to adjust my target level to something more like 3.3V or 3.4V.

I like my titles to match for all places where I publish. This is not the first article with a question in the title, there is also this one: My charger do not charge LiIon to 4.2V, is it faulty? about low charge voltage, it was from there I got the idea for this article.

Anyway people looking for information will probably open a thread with a question title, to see if it has a good answer (At least I hope so).

Thanks HKJ. Again advice we should all heed.

Great info! Thanks

I would suggest “How far can LiIon be discharged? (detailed answer)”

Thanks for this interesting data HKJ.

I've recently been giving some advice on FastTech's forums to certain users concerned about the safety of using unprotected batteries on single-cell (1SxP) buck driven led flashlights. Since the absolute minimum voltage a typical (Cree) led would drop for any current to flow is 2'5V (checked XM-L/XM-L2 datasheets), my conclusion is that it is pretty safe. It must be understood that, as we approach that voltage, current flow diminishes exponentially: it'd take “ages” to reach there (and it would be undeniable to notify on the light's output.

It is a bit surprising to me to see such a jump between load and “no-load” (voltmeter…) voltages in your measurements for that current flow, because that would mean there's close to 0'4Ω of resistance among:

{ R = (Vnoload - Vload) / I }

  • The battery's internal resistante (supposedly lower than 0'4Ω).
  • Whatever stuff between the battery terminals and your readout locations… ?
  • Am I missing something?

Hope the expounded above helps.



This question is asked a lot on the forum so will ask here.
If the batteries voltage is measured less than the recommended minimum does it make any difference to the chemistry and safety of the battery if its discharged below the limit very quickly or slowly, for eg in a flashlight that has very low parasitic drain?
Many are tempted and it is often mentioned that it is safe to recharge a battery if it has been drained below the recommended voltage slowly.
Hope that all makes sense.

Draining slowly mean the battery spends more time at the lower voltage, i.e. more damage.
But as I say above the 2.5V or other end voltage is not the danger limit.

Well, I’ve barely read a thing about those Nyquist plots, yet anyway, that explains “everything”. Thank thee. In such a case, that just confirms (my) the predicted safety of using single (1SxP) buck driven li-ions led flashlights because of their minimum (led) Vf, which coupled with the intrisically higher internal impedance of the battery when approaching that low Vf… means it is even more difficult for the battery to reach “that low”. Hope this is understood my dears. :laughing:


What would your advice then be for discharging phone batteries to ensure a proper calibration of them?

For instance, I am using an iPhone 6 Plus. I read that the battery should be completely drained once per month. However, I read online that it is unwise to completely discharge the battery (run the iPhone on max brightness and play a video with max volume till it shuts off).

I, for now, don’t let my battery drop below 10. I just wonder how I can fully calibrate it by letting the capacity of the battery drain fully so I can charge it from 0-100 and have the highest accuracy of calibration for the said battery.

You only need to calibrate it if your believe the remaining time is far off.
A full discharge/charge will allow the fuel gauge to recalibrate itself, these chips are counting mAh into and out of the battery and this will go out of calibration over time. Some of the newer chips can also correlate with battery voltage and do not need much calibration.

I’ve not done a “battery calibration” for months on my XT1032, and still it shows me accurate enough charge estimations… :sunglasses:
I minimize battery wear by not charging it above 60%, generally. See here:
BU-808: How to Prolong Lithium-based Batteries
Additional information: in the article it is reported that, for 4’2V maximum voltage li-ion chemistries, 3’92V or below no-load voltages are reported to do away with all voltage related stresses. 3’92 / 4’2 equals 14/15 so I’d use this fraction to determine/estimate this equivalent voltage for the now commonly used higher maximum voltage ICR chemistries (commonly used in modern mobile phones).

Stupid myths and [censored] seem to abound everywhere. :person_facepalming:

Your device’s battery is completely firewalled through its power management circuitry. That means in no [censored] way will it allow the battery to be over-discharged.
I bet the lowest no-load voltage your phone’s battery has ever seen is fairly above 3V. I’ve never seen below 3’1V (load voltage, which is always higher than no-load) through my battery monitoring software before a forced low battery system shutdown.
What is more: what you call a “charger” is not really a charger but, usually, just some kind of more or less capable constant voltage supply with @#$% gimmicks.
The aforementioned power management circuitry inside your device decides what/how and when whatever crap is done: “negotiates” power input with the PSU/charger for up to the required amount, feeds the device’s internals and then uses the remaining power to charge the battery.

How could they, the manufacturers, gladly offer the kind of device warranties you seem to enjoy in these iCraps, Crapdroids, Wincraps, etc. in the hands of uneducated [censored] morons without this kind of sophisticated power management? :person_facepalming:

Well, hope this is properly understood. Maybe I should write a sticky about this somewhere, for the love of @#$%…


Yes, I meant exactly that. According to the previously alluded article at Battery University, just around 58% of remaining battery capacity is held at 14/15th of maximum charge voltage (3’92 out of 4’2V).
My battery is a 3’8V nominal unit, and, at most, I see just below 4’33V full charge voltage. At 60%, I can guarantee you I’m obtaining 4x the estimated battery life expectancy since for every reduction in (nearly) 0’1V maximum battery voltage it is estimated the cycle count doubles. So I attain 8x the cycle life at above half of the useable battery capacity: guaranteed 4x typical battery life expectancy.
And no, it is not inconvenient for my optimized rooted system: I consistently attain above 3 hours of SoT (screen on time) with just ½ of the battery capacity.
Moto G 2013 XT1032 running stock über-optimized “Crapdroid” Lollipop v5.1.
Hope this helps. :cowboy_hat_face:


How do you get it to stop charging at a certain percent?

Thanks HJK for the info :slight_smile: it seems that the cells fall-off at the 3volt average mark then rapidly dropping to the 2.5 volt, but the rebound is quick when the load is switched off.

Yes thank you HJK. I wonder why low voltage cut off is not at 3volts? No real power left so flash lights should shut down to save the cell