How to TEST 18650 cells (DIY Powerwalls)

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

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.

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!

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

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

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

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

What’s your recommended capacity tester? I didn’t notice a brand/model when you showed your discharge tester.

lovin' this vid. Listening and will continue again and again. Love the learning here

Awesome tests. thanks

Thanks for sharing this info! Great content

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.

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

Eres un crack Jehu !!!! Saludos ...Thanks,...

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

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.

Awesome vid

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.

This really helped

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.