How to Determine Battery Condition/Age

[akksnv]

I have an external battery charger for my 18650s that tells me the voltage when I put them on the charger, as well at the voltage when I take them off and how many mAh's were "charged back in".

I have a Samsung 25R that was reading dead on my istick Pick Mega, I believe it said 3 or 3.2v when I put it on the charger and it said 1933 mAh when it was fully charged. I think the problem is I don't know how many mAh's would have already been in it at 3-3.2v, otherwise I would know 2500 mAh total capacity - X mAh at 3-3.2v = Y mAh that should be charged back in.

Sorry if this is a little confusing or poorly worded, I'm still working on waking up this morning Any help would be greatly appreciated.

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[bombastinator]

Part of the issue is how much risk you are willing to tolerate.
the way i personally test a battery is to see how many volts it is holding when charged and then take it out of the charger and let it sit for a day, then test the voltage again. It should hold near 4v and hold that charge. If it doesn't the battery goes in my unsafe pile which I will only use at home. If they get below 3.5v I toss em.

also important for safety is the battery sleeve. The plastic wrap around the battery is an important \safety feature that prevents shorts. if it has holes in it i replace the sleeve (they're cheap heat shrink tubes) and test the battery. YMMV. I think of my practice as a minimum standard. a lot of people have much stricter standards about battery safety than I do.

 

[DaveP]

You'll hear people say that an 18650 can be charged down to a minimum anywhere from 2.5v to 3v. The lower you discharge the more you stress the battery. I get something like 2200mah to 2500mah on a 25R after charging on my xtar VC4. Charging usually reads 3v to 3.2v when I insert it after the mod declares it dead.

I've had mods take a battery down as low as 2.9v before shutting off. 3v to 3.2v may be a safer minimum for longer life.

Vape time is a better standard to judge whether a battery needs to be replaced. If it always took you far into the day and then begins to shut down several hours early, it may be time to replace it.

 

[akksnv]

Sorry, I should have clarified, I realize there's definitely a safety aspect to this, how low you run your batteries, how many watts you vape at, etc. but my question was more about when a battery is old and not holding a charge like it should, and not about when it should be considered unsafe.

Having said that, it does seem like my batteries aren't holding a charge as long, however it's kind of hard to tell because it's a slow, gradual change over a year or more. To further complicate things, increased usage would also reduce how long the battery lasts (without the battery necessarily being in any worse condition).

That's why I wanted to look at numbers as "hard proof" as to how my batteries are doing. I've had them for at least a year, and I'm pretty sure a "full" charge now isn't what it used to be, but I'm not sure if it's 95% of what it used to be or 50%. It seems like my charger tells me everything I need to know to determine this, I just don't know how to interpret it :/

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[bombastinator]

Sorry, I should have clarified, I realize there's definitely a safety aspect to this, how low you run your batteries, how many watts you vape at, etc. but my question was more about when a battery is old and not holding a charge like it should, and not about when it should be considered unsafe.

Having said that, it does seem like my batteries aren't holding a charge as long, however it's kind of hard to tell because it's a slow, gradual change over a year or more. To further complicate things, increased usage would also reduce how long the battery lasts (without the battery necessarily being in any worse condition).

That's why I wanted to look at numbers as "hard proof" as to how my batteries are doing. I've had them for at least a year, and I'm pretty sure a "full" charge now isn't what it used to be, but I'm not sure if it's 95% of what it used to be or 50%. It seems like my charger tells me everything I need to know to determine this, I just don't know how to interpret it :/

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Well as long as a battery dry is safe it becomes a question of how annoying it is to have a battery that isn't as full as it used to be. Toss em if you feel like. Hard proof is hard to come by as vaping varies so much by individual. You've got too many variables.

 

[Baditude]

...my question was more about when a battery is old and not holding a charge like it should, and not about when it should be considered unsafe.

This guy (Mooch) knows his stuff about batteries. Here's his opinion on when to discard your older batteries:

• When should you replace a battery?

 

[Rossum]

the way i personally test a battery is to see how many volts it is holding when charged and then take it out of the charger and let it sit for a day, then test the voltage again. It should hold near 4v and hold that charge. If it doesn't the battery goes in my unsafe pile which I will only use at home. If they get below 3.5v I toss em.

IMO, a cell that self-discharges to 3.5V in a day is well beyond "unsafe". There's no reason for a good battery to lose more than a few hundredths of a volt per day.

 

[Train2]

Not real complete, but easy...
Does it still charge to 4.2?
Almost alway, after about a year or so (depending on how many I have in rotation), my older batteries will only charge to 4.18. Then 4.12, etc... This drop in "capacity" is noticeably linked to the run-time. They'll run down much faster at about the same age.
That's when I start thinking about getting new batteries.
And once I have plenty again, I start taking the oldest - or the ones that provide a noticeably short run time - out of rotation. I'll often keep a few as "backup" but since I just got 8 batteries in yesterday, I'm gonna thin the herd this week...

Sorry, I should have clarified, I realize there's definitely a safety aspect to this, how low you run your batteries, how many watts you vape at, etc. but my question was more about when a battery is old and not holding a charge like it should, and not about when it should be considered unsafe.

Having said that, it does seem like my batteries aren't holding a charge as long, however it's kind of hard to tell because it's a slow, gradual change over a year or more. To further complicate things, increased usage would also reduce how long the battery lasts (without the battery necessarily being in any worse condition).

That's why I wanted to look at numbers as "hard proof" as to how my batteries are doing. I've had them for at least a year, and I'm pretty sure a "full" charge now isn't what it used to be, but I'm not sure if it's 95% of what it used to be or 50%. It seems like my charger tells me everything I need to know to determine this, I just don't know how to interpret it :/

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[akksnv]

Well as long as a battery dry is safe it becomes a question of how annoying it is to have a battery that isn't as full as it used to be. Toss em if you feel like. Hard proof is hard to come by as vaping varies so much by individual. You've got too many variables.

I know how annoying it is right now, but I don't know how less annoying it would be with new batteries (ex. are my current batteries charging up to 95% of the original capacity so new ones wouldn't make much difference, or are they charging half as much as they used to and new ones would be a big improvement). Also, I should be able to tell what kind of condition they're in given what my charger tells me. I know the battery originally held 2500 mAh and charges 1933 mAh back into it when it's at 3v, but I don't know how many mAh's I'm starting at with 3v.

This guy (Mooch) knows his stuff about batteries. Here's his opinion on when to discard your older batteries:

• When should you replace a battery?

Thanks, yeah I know Mooch knows his stuff when it comes to batteries, I was kind of hoping he would chime in I have a feeling he probably knows the answer I'm looking for. That post looks like it only has more general info, though, and not an answer to my question.

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[akksnv]

Not real complete, but easy...
Does it still charge to 4.2?
Almost alway, after about a year or so (depending on how many I have in rotation), my older batteries will only charge to 4.18. Then 4.12, etc... This drop in "capacity" is noticeably linked to the run-time. They'll run down much faster at about the same age.
That's when I start thinking about getting new batteries.
And once I have plenty again, I start taking the oldest - or the ones that provide a noticeably short run time - out of rotation. I'll often keep a few as "backup" but since I just got 8 batteries in yesterday, I'm gonna thin the herd this week...

I see, so when the capacity starts dropping, they won't charge to 4.2v anymore? I was thinking it would still show 4.2v but there wouldn't be as many mAh going in, if that makes sense (note: I'm no chemist, or Mooch )

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[Rossum]

Does it still charge to 4.2?
Almost alway, after about a year or so (depending on how many I have in rotation), my older batteries will only charge to 4.18. Then 4.12, etc...

I see, so when the capacity starts dropping, they won't charge to 4.2v anymore?

I don't think this the correct way to state the issue. A charger will charge cells to 4.2V. A properly designed one (which is effectively all of them) supplies constant current until the cell voltage reaches 4.2V, then holds 4.2V while monitoring the current the cell accepts, and will stop charging when the current (at 4.2V!) drops below a certain threshold (generally 50-100 mA).

So what we're really talking about here is what happens to the cell voltage after the charger stops charging. Does it stay at or (or real close to) 4.2V, or does it drop? If it drops noticeably, how much, and how fast, and does it continue to drop each day you leave the cell alone, or does the voltage stabilize?

FWIW, I do believe the amount drop after a cell is charged is an indication of its internal health. The less (and slower) the drop, the healthier the cell is.

 

[Barkuti]

As far as I understand, performing a measured discharge cycle over a cell and comparing this figure against reference values (own brand new self test numbers or those provided by reputable reviewers) determines the level of wear it has. At comparable discharge rates, of course.
Example: let's say a VTC5A measures those 1.933mAh you spoke about at 1A, a cell which yielded 2480mAh in HKJ's tests. Thus, such cell would be at (1933 / 2480) × 100% = ≈77.94% of its original state, both capacity and discharge performance wise.
Hope this is of help. ( ͡ᵔ ͜ʖ ͡ᵔ )

 

[Hawise]

For what it's worth, I get ~2250 on my 6-month-old 25Rs. It wasn't much (if anything) higher when they were new.

I'm using a different mod (Evic VTwo Mini) so the cutoff may not be identical.

 

[akksnv]

As far as I understand, performing a measured discharge cycle over a cell and comparing this figure against reference values (own brand new self test numbers or those provided by reputable reviewers) determines the level of wear it has. At comparable discharge rates, of course.
Example: let's say a VTC5A measures those 1.933mAh you spoke about at 1A, a cell which yielded 2480mAh in HKJ's tests. Thus, such cell would be at (1933 / 2480) × 100% = ≈77.94% of its original state, both capacity and discharge performance wise.
Hope this is of help. ( ͡ᵔ ͜ʖ ͡ᵔ )

Thanks, I think this is kind of what I wanted to confirm, although comparing a 25R to a VTC5 probably isn't the best comparison (which leads me to the next reply)...

For what it's worth, I get ~2250 on my 6-month-old 25Rs. It wasn't much (if anything) higher when they were new.

I'm using a different mod (Evic VTwo Mini) so the cutoff may not be identical.

Thanks for the numbers. I would assume the cutoff is pretty similar, and 6 months isn't too extremely old... it's at least something to compare against.

So between these two replies, it sounds like it should be getting closer to 2250 mAh after a full charge, but is only getting 1933 mAh, therefore I'm at somewhere in the neighborhood of 85.9% of its original state (or, more accurately its 6-month old state).

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[Spey]

I see, so when the capacity starts dropping, they won't charge to 4.2v anymore? I was thinking it would still show 4.2v but there wouldn't be as many mAh going in, if that makes sense (note: I'm no chemist, or Mooch )

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Thanks, I think this is kind of what I wanted to confirm, although comparing a 25R to a VTC5 probably isn't the best comparison (which leads me to the next reply)...Thanks for the numbers. I would assume the cutoff is pretty similar, and 6 months isn't too extremely old... it's at least something to compare against.

So between these two replies, it sounds like it should be getting closer to 2250 mAh after a full charge, but is only getting 1933 mAh, therefore I'm at somewhere in the neighborhood of 85.9% of its original state (or, more accurately its 6-month old state).

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Without using hard numbers, minimal accurate information is gained.

Example:
1) In your OP you stated you were not sure if voltage at start of measured charging was 3.0v or 3.2v.
2) Without having a reference to performance when battery was new, no accurate way of determining % of degredation.
3) Without knowing the cut-off voltage related to battery capacity measurements you have nothing to compare to. I have read that Samsung 25r battery capacities (specification related) are based on 2.5v cut-off values, and that one of the significant performance characteristcs is their low voltage performance (and you are measuring from 3.0v or 3.2v).
4) Age (6-month references, etc.) really should not have much value. How many charge cycles and conditions if usage are what effect battery degredation performance. Example: I believe Samsung 25r spec. states after 250 cycles performance reduction 60% (this could be 6-months for one person or 2-years for another).
5) Unless you are measuring & testing consistently, accuracy of any values are ...?

I don't mean to come across as negative, and I like your questions and considerations related to where you're coming from. I used to take every new/used vape/light battery I had and measure mAh inputs (charging) from a known beginning voltage. Write these numbers down, and compare over time as a means to measure wear. The goal of the experiment should include minimizing your variables, to achieve any valuable data and testing degredation over time and or to a known specification (manufacturer or self-created).

 

[akksnv]

If anyone is interested, I did end up getting two new 25Rs so I made sure to get some information after charging.

The old batteries are about a year old. I put one on the charger when my pico wouldn't fire anymore. It read 3.0v, charged up to 4.2v, and said 1857 mAh were "charged back in".

The new batteries came, I charged them completely (they were at 3.5v when I got them, charged to 4.2v) then used one until my pico wouldn't fire anymore. I put it on the charger, it read 3.0v, and when it was done it read 4.2v and said 2530 mAh (!!) were "charged back in".

So that means my old batteries were holding about 73% of their original capacity. I could also tell a difference in that they not only lasted longer, but also continued giving good hits for longer (ex. didn't get weaker 5 hours in) and even when they we're about dead, the hits were still pretty good (I can hardly get a hit with my old batteries when they're about to go dead).

Suffice it to say it was a $13 well-spent haha

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[Spey]

akksnv,

It would be my guess that if you were to watch the firing voltage drop of the batteries (from resting voltage to firing voltage), you would see a significant difference between the old and new batteries (greater drop on old batteries). The why of why the new batteries hit stronger even when both read same resting voltage.

Record starting charge voltage and mAH to 4.2v for future test evaluation of those batteries.

Pleased to read solution as simple as battery replacement.

 

[nevin]

As pretty much everybody has said, in one form or another. You can't use the rated/sticker capacity compared to the capacity put back into battery from the charger as an indicator of how long the battery will last or it's health. I know exactly what you're talking about as I've thought of the same thing looking at my charger once. That number is only what has been replaced, not the total capacity. And can fluctuate greatly depending on a number of variables. Voltage when taken out of device, how long it sat before being put on charger, etc.... these will all effect that mah number you see on your charger.

If there is voltage drop the day after a charge it's a good indication that things might not be working as well as expected. And will probably be the easiest "hard proof" to verify.

Yes there are more complicated tests you can run, but if you didn't do them when the batteries were new, you'd only be comparing it to someone else's bench test of their new cell. If you are looking for a true comparison.