Authentic Tomo M4 Portable External Battery Charger Box (Batteries Not Included) & 2-USB Ports DIY Battery Bank Premium Plastic Shell Box with LCD Display

I've bought this Tomo 18650 battery pack/charger twice. I loved the *idea* of it - a battery pack that can charge your phone(s) using commonly available 18650 Lithium Ion batteries. When it runs out of juice, you can just swap in a couple of fresh 18650 batteries and be on your way. But in reality, these Tomo chargers are really flakey. They sometimes work, sometimes don't.At one point, one of the USB output ports worked well (the one closer to the microUSB charging input), charging my Galaxy S10 at a consistent 1.4A, while the other one was iffy. But over a few weeks, the whole thing just got flakey, with the screen flashing on and off, the power cycling on and off, and the connected phone charging very slowly.I would have written this off to a defective sample, but it actually happened twice. The first one failed outside the return period, so I bought a second one, only to have the exact same problem occur. I purchased both on Amazon.Pros:* Can charge your phone using 18650 Lithium Ion batteries* Allows for "passthrough" charging - charges phone while the charger itself is plugged in* Works with anywhere from one to four 18650 cells on boardCons:* Doesn't last more than a few weeks, even when handled gently* See aboveAgain, I love the idea of this product, but the execution - the actual product - sucks.

I did a bunch of tests on this, and the more I've used it, the more I have concluded that this whole thing is overpriced junk. Aside from the fancy display, the performance of the electronics themselves are very poor. My tablet is only willing to draw around 570mA when charging from it, whereas even power banks half the price will charge it at 1.2-1.5A easily.Measuring the voltage with an external voltage meter (known working because I have used it to test other units just fine), the voltage drops to around 4.63V under not even a 1A load, even though the display on the unit itself keeps showing 5.11V regardless of what load I put on it. This would probably explain why my tablet does not draw more current from it. The current metering on the power bank's display does match my external measurements, though. I would not consider this usable to 2A, as the voltage sags far too much. If I load it with only 1 cell, the load drops even further and cuts off entirely before 2A.It also has a tough time detecting loads when I connect them, and will just pulse the output even when something is connected, forcing me to manually press the button and "tell it" the load is there.When tested using cells of known capacity (measured using the NOR test of an Accupower IQ338 charger) and drained using a constant resistive load at ~1A, I estimated the conversion efficiency to be roughly 77.5%, and that is being generous considering the low voltage. For reference, based on similar testing, I usually get around 82-85% efficiency for most good quality power banks I have tested, so this one is particularly poor. I had wanted to test this using a bench power supply instead of cells, but for some reason the power keeps resetting if I try to run it under load from a bench power supply.Overall, I like that the compartment can be opened and closed more than once rather than snapping together permanently like some power banks, but the poor voltage regulation and low efficiency make this a hard pass from me. Save your money and look elsewhere. For a lower price maybe, but I had expected a premium product for the $18.55 price tag I paid.

I've used it enough to finally see what the product is capable of. This charger is a fantastic idea. However, I noted multiple issues with it. Independent charging/discharging circuit sound like a great safety feature. Not working well though. Batteries overheat rapidly with high currents (charging or discharging). I do not have this happening when using 4pcs 18650 cells paralleled (same sourced cells). Thus I cannot trust to leave it unattended fearing battery damage or even fire. Another issue is when a device finishes charging using this battery, it keeps restarting charge cycle and keeps looping charging/full, charging/full, charging/full and on and on.... So, in case of an iphone you hear tone/beeping start and stop charging every few seconds until you unplug the phone. Very annoying. Especially when charging through the night. Not a big deal but wish you could see battery level when charging other devices.

Bought this November 2018 and by January i was buying a new charger. I used this for 18650 batteries. I would put them on charge , it wouldn’t charge. I’d readjust the charger and it would say it’s charging , come back 20 minutes later to it not charging again. Even when it said it was charging 95% of the time it wasn’t. It would say the batteries were full and they wouldn’t be but maybe 25% charged. I’d highly suggest spending the extra money for a better charger. This was just a waste of time and money.

So...important note... if you want to keep 4 fulled charged 18650 batteries in this...and ready for emergencies... you must put a piece of paper into the unit to cut off connections from the batteries to the unit. I dropped this in my backpacl...initially... totally turned off... but it slowly ran my batteries down to zero. So 8 months later...I was toast. Not good in an emergency. So Charge batteries, THEN insert batteries and wedge a piece of paper ... or thin plastic along one side of the of the battery connections. That was the unit doesn't slowly kill the batteries. This is commonly done on product you buy thaty have batteries pre-installed. Same thing. Batteries tend to discharge themselves anyway... but this will give you the best chance for success.