Same seller that I bought from.
I haven't cracked it open to investigate. I may do that to figure out a
way to get around the always powered on. It could be that my particular
battery bank has a low trigger point.
You actually may be right about the efficiency. Good points. I will have
to investigate further. But for $12, it was a cheap solution. I am
certain that I could do better with a custom design, but not for
anywhere close to $12.
And outside of the flat response (though it is not THAT flat) a battery
pack already has a boost circuit in it to go from the 4.7V lithium
voltage to 5V. So it will likely hold it up to 5V until the very end. So
there probably isn't any visible drop until it shuts off. I didn't
consider that.
This does raise an interesting idea, though. Instead of using the switch
in the power jack to disconnect the batteries, perhaps a mod is in order
which can just switch over to the alkalines upon external power
disruption. This is usually a pretty simple circuit like you would find
on an arduino which chooses USB voltage or DC input based on which one
is greater.
On 10/21/2025 5:39 PM, B9 wrote:
That looks great, thanks for the link!
The one you linked is the same seller as the one you tested, right?
I'm always suspicious of stuff on Amazon these days. No idea if it's
going to do something out of spec, not work at all, or simply catch on
fire.
I am surprised that the design is such that the cable itself is
drawing non-negligible current from the USB battery. Have you measured
actual wattage? I thought most buck/boost chips had low "quiescent
current" modes, but I'm no expert.
If it was designed poorly, the conversion to 6V might be inefficient
and I suspect you'd actually get better battery life by just using the
5V from the USB directly.
Even with an ideal circuit, I'm curious how much extra life, if any,
one gets by increasing the voltage to 6V. The lithium ion voltage
curve is mostly a flat line and then a precipitous cliff at the end.
That's why you can't trust the red low power light on your Model T to
give enough warning with LiIon batteries. What's more LiIon batteries
have an internal discharge cutoff point to prevent damage due to low
voltage.
Or so I've read. (This is not my field of expertise and I do
appreciate any corrections.)
--b9
On October 21, 2025 1:19:24 PM PDT, Scott McDonnell
<[email protected]> wrote:
I am going to bet that somebody already found this, but I will
tell the group about it just in case. If you are looking for a
power adapter to run your M100 from a USB battery bank, this is
the ticket: https://www.amazon.com/dp/B0BJDRV4H5 Boost to 6V and
it is already center negative so you don't even need to crack it
open and flip the wires. Of course, you can run the M100 from the
5V directly, but you will get more life out of this as the M100
shuts down at 4.8V from my understanding. The only drawback is
that it will draw power from your battery bank the entire time it
is plugged in since it draws enough current by itself to keep the
battery bank turned on.
