How to TEST 18650 cells (DIY Powerwalls)

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FAQ:
8) Why not use Supercapacitors?
A. Batteries work better at this time, caps are rare and expensive devices that are very good at doing things not needed for storage systems typically.
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[DennisGentry]

First, I think it's great that you're doing this empirical testing. However, when it comes to temperature, you're doing it wrong. The datasheet is not claiming that the battery temperature will stay under the max temperature under all load and ambient temperatures. It's telling you that you are damaging the battery when you let it exceed that temperature. It is your responsibility to either cool the battery or else stop drawing so much current.

It is true that good quality batteries will have low internal resistance and generate less heat at the same power output as worse quality batteries, so there is some correlation between good quality batteries and those that stay cooler, but that's incidental, not a claim of the datasheet. Heat is generally the enemy of batteries, from lead-acid to nickel metal-hydride to lithium. Keep your batteries cool! Good luck!

[honpsu]

Temperature rise depends of your ambient conditions. The temperature spec gives you operational limits you should operate the cells. If the cell surface temperature rises over the spec (for example in ambient 40’C conditions), YOU MUST ACTIVELY COOL THE CELLS during charge/discharge and/or LIMIT the current/loading! 8A discharging is allowed up to the surface temperature limit - it doesn’t mean that the cell would be out of spec.

And where’s all comparison of SAFETY and lifetime related? SAFETY CERTIFICATIONS (UL, CE, TÜV, ...), safety devices integrated in the cell and are they really working and preventing fire. Lifecycle cost per Wh is not the same if a cell lasts 50 cycles compared to a cell lasting 2000 cycles, especially in powerwall application.

[roberthill]

Just be careful they haven't given you the best ones first then diminish the quality later on.

[mmReefs]

Jehu, thanks for still wearing the "Power 2 Puerto Rico" shirt. It means a lot for us in the island!!!

[Bill]

You've gone MAD with power Sir.
UP with the struggle of the IR ( Internal Resistance ).

[cmuller]

You should never let cells reach those high temperatures. So you have to use a cooling system. The closer to 25C the better. The problem is that those measures are for a single cell in free air. But imagine what happen if you pack many of those together...
The problem is that using cells at high temperature generates some internal side chemical reactions (unwanted) that destroy them progressively. So the capacity will drop rapidly over time and may even drop sharply if the electrodes end up being plated / covered by side reaction byproducts blocking normal reactions.
Unfortunately evaluating the rate of those reactions is hard to test without very high precision equipment.

[RonYason]

Just a newbie with the interest with powerwall. really great stuff sir..

[haroldsy]

One of the ways I identify or classify a battery to be on the better side is to weigh them. Manufacturers usually decrease the raw materials making them lighter. With the same materials used like both have metal cover and same "mah" capacity, you can now compare them.

[khaleef_hrm]

Jehu is now my Favorite 18650/Battery/Power YouTuber. No other comes next.

[aljanobin]

Great video, but I want to note the operating temperature is based on your environment.
You are not supposed to allow them to go above 60C not that the cell can't go above that.
So in your case you should add more cooling and not allow the cell to go above that temperature.

[bro]

I do safety testing (short circuit and overcharging) on commercial 18650 and 21700 all day. I would never use any of those cheap cells. I’ve seen too many of them vent (at best), explode (at worst). I would never let them get above 70C on a charge or discharge. Even using good ones, all it takes is one mistake and your house will be gone.

[NexiTech]

Great video and very useful info! Thanks. Keep the great work

[theone]

Milliamp spec, temperatures spec, and short term test of a battery does determine a good battery. It's the quality and long term use determine a good battery

[stephentaylforth]

Quick and dirty - weigh the damn things. Fakes are almost invariably light. Testing is far better obviously but weighing them will catch a lot of crap before you get involved in testing. If you're running a powerwall the IR is often secondary as typical load is usually fairly low per cell. Pulling 10 amps per cell will discharge it in a few minutes. A powerwall that goes flat in 20 minutes isn't much use. It goes without saying don't buy anything with fire in the

[LarryLaPine]

Thank you. I am looking to make some e-bike batteries and other projects. Aside from the oe brand of 18650 batteries do you have recommendations as to type and brands of other materials, gauges of lead wires, nickel strips, fish board etc.

[davidbanwell]

Thank you you have cleared up a lot of my questions about safe loads on charging Batterys.

[vraymond]

Sorry to say, I ain't expert on battery, but I think the temperature 10:33 is the "recommended" temperature for the battery to work on, just in case if you expecting to get more energy. i.e. to get the best performance from the battery, Please actively maintain the batteries' temperature between -20°C to 75°C max, recommended to actively (fan) keep battery below 60°C during discharging. Please correct me if there is anything that doesn't make sense to you. Also, you should have test compare their charging cycle limit and degradation rate as well.

[Mazel_Tov_]

I see you put a lot of hard work and effort into you videos. top notch much respect.

[dennisyoung]

Good. I’m hoping to start doing up my own “emergency suitcase batteries” within the next 18 months, and the same for “monstrous bike batteries.”

[frankbumstead]

Well done, interesting that well known Manufacturers are not necessarily the best. I have bought a small number from a UK distributor and so far they Check out OK on capacity after a few cycles through the Charge / Discharge equipment I'm using. Sinowatt 34MP 3350mAh 18650