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Red Sanyo 18650 Cells Getting Hot While Charging
We have all experienced the heat phenomenon behind the Sanyo 18650s in one way or another. So what's the deal with these cells? What is wrong with them? I have tested close to 3000 cells now. I try to charge them up to 4.2v for capacity testing and I would estimate at least 50% of the time, they get scalding hot around 3.9v.

Points of interest...
* They all have a healthy voltage coming out of the packs.
* I tried all kinds of charge currents between 0.25A and 1.0A. It doesn't seem to matter.
* Recently someone suggested letting them sit for a bit then trying again. I stopped them around 3.9v when the got hot, let them sit overnight, then put them back in. They charged up to 4.2v just fine without heat this time. They discharged normally to 3.0v. Then on the recharge cycle, they got scalding hot again.
* It can't be an "old chemistry" that limits them to 4.10v since they get hot well below that.
* For those of you who are going to say "don't use scavenged laptop packs", this statement carries no weight here considering it only happens with the red Sanyo 18650s, and approximately 3000 cells of mixed brands have been tested.

So what's the deal? Are they just cheap garbage? We have all experienced it, yet I see very few hypotheses.

stefan1025 likes this post
I'm not a chemist - but it has to be the chemistry within that has been degraded by use/abuse.

When new the "chemistry" will allow an applied amount of energy to be stored, and released later on demand - during this process of energy storage (charging) the voltage will rise - at a certain point, the charger will see the voltage rise and cease applying energy.

When past its prime, the "chemistry" will be unable to either receive or release energy - the inability to release energy is shown by capacity testing - the inability to store energy is shown by the inabity of the chemistry to convert applied energy into a voltage rise, which is seen by the charger as a cell that isn't fully charged - so it keeps applying energy.

If that energy isn't being converted by the "chemistry" into a stored form, it'll be wasted and converted into heat.

Those red cells don't because warm/hot over a short period of time - all of the ones I've had have taken a good few hours,, which would take them far past the point at which they should have been fully charged - and because we are mostly using smart chargers that sense voltage and current delta, they'll never see the expected charge profile - so they keep pumping in the amps.

Which is why nearly all chargers have cut off timers.
mike, DCkiwi, BlueSwordM like this post
Hi mike,

I'm quite new at this 18650 recycling process, but the first thing that I've noticed was the bad quality of this cells:

- A lot of heat (45ºC) charging at 0.5A;
- Almost impossible to charge up to 4.2v (from my point of view isn't a problem, but this fact brings a huge voltage drop (>0.1v) in 3 or 4 days without using it. Resuming: I made 4.0v charging, 4 days after I've checked it again 3.85v);
- The internal resistence is always high (300mOhms)
- For last but not least, i found the major part of this cells inside Toshiba laptops with flowing lable (Rev 1.0 6 Cell Recycle, you can check in the image). So, I've some concerns about the recycling process adopted.

I've a a lot of this cells and I'll not use them in a powerwall.

Best regards,
BlueSwordM and Dietmar Rheeder-Kleist like this post
I've had many Sanyos that don't wait until the end of charging to get hot. Usually if they're going to get hot it's within 10-15min of being on the charger. Most of the time if they don't go above 110f/43c i just let them cook a bit and see what happens. A lot of the time they stay a bit warm but still complete. Once they get up to 140f/60c to the bin they go.
Dietmar Rheeder-Kleist likes this post
Off Grid Setup
3 - 320watt 24v Panels - MPPSolar 2424LV-MSX - 672 Cell 96p7s 5.5kw Power Wall

Retired pack 2kw 420 Cell

On Grid Setup
44 - 250 Watt Panels with Enphase micro inverters
Hi again,

This is an example of a Toshiba battery that I've mencioned before (was my first post, so url were disable to me  Smile ).
[Image: rec.jpg]
(01-24-2017, 05:42 PM)DanielD Wrote: - Almost impossible to charge up to 4.2v (from my point of view isn't a problem, but this fact brings a huge voltage drop (>0.1v) in 3 or 4 days without using it.

Whats your logic behind thinking an inability to reach its fully charged voltage isn't a problem ?
Dietmar Rheeder-Kleist and mike like this post
(01-24-2017, 06:19 PM)Sean Wrote:
(01-24-2017, 05:42 PM)DanielD Wrote: - Almost impossible to charge up to 4.2v (from my point of view isn't a problem, but this fact brings a huge voltage drop (>0.1v) in 3 or 4 days without using it.

Whats your logic behind thinking an inability to reach its fully charged voltage isn't a problem ?

Yep, It's a indication that the cell isn't very good. I've not explained it very well... Sorry  Smile
I was trying to say that, if you want to use that cell for a powerwall with a max voltage per cell of 4.0v, you could avoid some heat. But, in the other hand i think that's not a good policy, because you're just hiding a future problem.

Best regards,
alfu, kazbach, Dietmar Rheeder-Kleist like this post
Recent video where someone looked at the capacity spread of all his cells.

I was reading somewhere Sanyo use a different electrolyte to other cell manufacturers, not found that article yet.
However I did find this technical teardown of various cells.
Quote:The difference between the Sanyo and the Panasonic cells are an increase in ohmic resistance (how much is the cell opposing the flow of current). This is due to the battery chemistry type, notably the electrolyte formulation which is outdated.

The videos shows two identical battery packs, one with a recalled part number, one without. Difference is the recalled one states it has Sanyo cells inside.
Al's Shed likes this post
"It has Sanyo batteries in it, which is a reputable manufacturer in Japan. Generally they make good cells"
Not sure what to think of that statement. LOL.

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