1s USB C BMS with step up to 4.5V a thing?

Got a kid on the way, and already I’m faced with a trinket which requires stupid disposable batteries. I figure I better get my battery hacking game sorted…

Found one of those dumb disposable vapes the other day while walking my cats, and liberated a perfectly good lithium cell from it… But 3.7V is probably a bit light on for something designed for 4.5V.

Anyone know of a BMS with USB charging that can also step up the output a bit? Or maybe there’s a seperate unit I can add on to a normal 1s BMS?

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Oh hey, this would probably be suitable, right?

I suppose most anything which takes three 1.5V cells should be happy enough with 5V?

… Although it doesn’t say anything about cutting off when the battery gets low. ETA: actually, the datasheet mentions the chip needs 2.9V from the cell to do boost mode. Neato

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It seems you’ve already made some headway in your search for a solution to power a device originally designed for 4.5V using a lithium cell from a disposable vape. Your idea of using a BMS (Battery Management System) with USB charging that can step up the voltage is a good one.

The MP2636 Power Booster & Charger Module you found could indeed be suitable for your needs. It’s designed for applications where lithium batteries are used as power solutions, focusing on power boost and battery management.

Since the device you’re aiming to power is designed for 4.5V and you’re considering using a 5V output from this module, it’s important to ensure that the device can safely handle the slightly higher voltage. Many devices designed for 3x 1.5V cells (4.5V total) can tolerate a range of voltages, but it’s always good to double-check.

The datasheet’s mention of the chip needing 2.9V from the cell to operate in boost mode is a crucial detail, ensuring that the module doesn’t over-discharge the lithium cell, which is vital for battery longevity and safety. Just be sure to confirm the current requirements of your device and match them with the output capabilities of the MP2636 module.



Hi All
If your device won.t handle 5V use a diode such as 1N400X series to drop 0.7V to 4.3V or so should be OK. Or maybe a schottky to get 4.7 or 4.8V if 4.3V is too low.
Cheers Bob


You’re likely to be faced with a lot of AA, AAA etc devices, you really might be better off investing in a few sets of rechargeable AA & AAA and a charger. You can also get batteries with USB-C ports directly on them.

However, none of that is as fun as repurposing and making your own. :slight_smile:

Actually, that MP2636 module is quite spendy compared to pairing a BMS with a step-up; each of which can be had for under a dollar… Reckon I’ll try that.

Whoah! What’s the search term for those?

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Hi Kimmo,

Found a guide on these:

And here’s an example that should get you closer, we don’t have any in our range though :frowning:


We do stock quality AA rechargeable cells and chargers though:

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Hi All
Can vouch for the Panasonic Enerloop AA cells (and charger). I don’t have any at the moment but some time ago I had 4 AA cells in a Fujifilm camera. Cell capacity seemed bottomless. On a trip to UK I took some 300 pics on a single charge.
Although the original was 4 X 1.5V alkaline cells @ 6V the camera did not mind the 4 X rechargeable @ 4.8V so the 300 pics at the reduced starting voltage is testament to the battery quality I think.
Cheers Bob

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Seems to work just fine without step-up.

Ended up going with a pouch cell from a laptop battery I couldn’t get going despite bypassing the BMS to get some charge in it… Maybe the BMS remembered it got dead flat? Anyway, the 1s USB C BMS was happy with it, charged it up to 4.1V… wonder how flat it can get before this gizmo won’t run

Hi Kimmo,

Glad to see you found a fix for your battery problem, always good to see solutions on posts.

Maybe you could make a sperate topic about your laptop battery to get to the bottom of that issue, if that was something you were looking into.

Great work.


I just bought another battery, and cannibalised the old one for the cells; that’s one of them in the photo above.

Yesterday I went through a pile of old phones, trying to see if any of them still worked, and had the same (or similar) BMS issue - phone wouldn’t charge, dug out the cell and bypassed the BMS (or is it just a PCB for a thermistor?) to get some charge in the cell, but once it had normal voltage, there was still nothing at the external contacts of the cell. This was the case for four or five cells - every one I tried.

Anyone have a clue why this would so consistently be the case?

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Hi Kimmo,

Typically a packaged cell will have a protection IC in it, and if it’s unhappy with the cell’s condition, it won’t let power in our out.

Have a look on the PCB in there for any tiny ICs, and maybe have a read of a datasheet of a protection IC to give you an idea of what you are up against:

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Yeah, I guess that would explain it… Oh well, I just have to bin those PCBs. Those little USB C charging modules are like ten for a few bucks though, and should be enough to stop me burning my house down, right?

It’ll be interesting to see how this 5Ah phone battery goes replacing four D cells… The little step-up PCB only had options of 5V, 8V(?!), 9V and 12V, so I went for 5V; seems to do the trick in this case.

Hey Kimmo,

Looks like you have a reasonable resolution there. Glad to see the project came to some fruition.


Just did a mouse yesterday