Lithium charging security

Don’t do this! (There’s a much safer way)

Big Clive discovered there’s a “thing” going around where people are charging lithium cells by attaching a stripped USB lead directly to them. Normally lithium cells are very safe if undamaged and correct charging procedures are used. But overcharging them like this can result in cell damage and potentially fire.

Some Lithium cells have built-in protection circuitry and some not. Many of the “found” lithium cells salvaged from disposable devices have no extra protection circuitry because it’s not needed in their application. But when recharging them it is very important to control the charge current and stop charging at around 4.2V

Direct charging with a USB lead has very little current limiting and the charger will often smash more than its rated current into them, potentially damaging the charger too. It will also keep charging them beyond 4.2V and that poses a genuine risk of internal chemistry damage, potentially resulting in avalanche failure where an internal short circuit occurs.
If that happens the full energy capacity of the cell will be released extremely quickly resulting in the electrolyte venting as a flammable vapour, and if sparks blow out too it can ignite resulting in a flamethrower effect. The real hazard is their ability to store and release very high amounts of energy. If used correctly and protected from physical damage, lithium cells are very safe.

Selected Viewer comments:

Wow, I appreciate that you took the time to write an in-depth and educational description for this video. I wasn’t aware that you could use the cell’s capacity as a measure for how much current you could push into a cell during charging. These “disposable” batteries are my first experience using lithium-ion cells for projects, so your videos on the matter have been amazing. Thank you for all you do :)

Basically “Please for the love of god, just use a Battery Management System board.”
Maybe it’s just my previous experience with lithium batteries, but charging a 3.7 (4.2v max) cell directly with a 5v USB connection with absolutely no overcharge/overvoltage protection is a very obvious recipe for disaster to me. I shouldn’t be surprised that there are plenty of horrible ideas circulating on the internet like undetonated land mines waiting for someone who doesn’t know better to come along.

I used to fly a lot of RCs and I had only one experience with a lithium cell venting randomly. I have gone through literally hundreds of them with no problem except for that one. And I’ve always used hobby grade RC chargers for lipo.

Any charge put into a rechargeable battery has to be governed in some way. The current has to be trickled in, not flooded in. Just connecting them up to a, ‘dumb’, USB connector is a very bad idea. As mentioned, it’ll overcharge the battery and cause it to become unstable to the point of bursting/exploding/catching fire.

Most lithium cells I’ve found in multiples devices have a small protection board, however I don’t to know to what extend it protects the cell other than charge current and voltage. If they have over discharge protection that’d be pretty awesome but for now I’ll just stick to the TP4056. Don’t wanna find out the bad way.

One important thing to keep in mind about the board with the TP4506 and the DW01: if you try to use it while charging the cell, the TP4506 will see the charge current as well as the load current and will never reach the charge termination point, potentially overcharging the cell.
So use that board to either charge the cell or protect it during use, but not both at the same time.

That’s very good information, especially since the protected one even have separate B+/- and OUT+/- terminals. From what I can tell fixing this would have “cost” three additional components and a very slightly larger PCB, it’s a bit sad that no one has capitalized on this to provide a better variant (that I can find, it’s all TP4056 with or without protection circuit, no PCBs that appears to be different).
Someone suggested that one could fudge a “load bypass while on USB power” using two schottky diodes (for lower voltage loss) – I may have to test that out next time I use one to confirm that this actually works but the idea looks reasonable (not a guarantee).

Maybe look at other chips from the same series. Some are designed to provide power output without the 10% loss in a schotky diode.

Most people want a pre-existing module so they don’t need to design their own, I doubt anyone charging a lithium cell with straight 5V would be capable of that. Which is why it’s a shame that the common protected TP4056 modules LOOKS like they support “pass-through charging” (separate B+/- and OUT+/-) but doesn’t – and that I couldn’t find any better (commodity, small, simple) pre-made alternatives, whether TP4056 or not.


  1. Tomi Engdahl says:

    Battery-Cell Charging Basics
    Feb. 23, 2022
    Understanding the basics of charging and discharging circuits for lithium-ion battery cells is key to proper contacting system design as well as successful manufacturing and testing of cells.
    Bob Zollo

  2. Tomi Engdahl says:

    Inside a combined power bank and jump starter

    I got this unit to explore it as an option for providing a high current 12V power supply for short term use. It’s a car jump starter and USB power bank. The 12V output is direct from the lithium battery pack with no protection, so care would need to be taken not to over discharge the pack when using it as a 12V supply.

    The connector is a standard EC5 high current battery connector, which is handy. The USB connector has floating data pins, so it may not be recognised by some devices.

    It’s a very modular design. A microcontroller that displays charge level and controls the buck regulator for the 5V output that is also used for the LED, and a current regulator for charging the lithium pack that has a three cell protection chip and matching charge/discharge control MOSFETs. One oddity is the use of the microcontroller to directly drive the charging buck regulator’s MOSFET.

  3. will james says:

    Lithium is mostly used in batteries to generate power and it is a great source of power. These lithium batteries are used in different commercial and household energy projects and it is do my essay legit to learn more about charging security. So while using these batteries you need to check the necessary precautions.


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