My DevTerm does not run on batteries. They are fully charged and the voltage shows over 3.9 volts (unloaded). When I hit the power button, the green light lights up brightly for a moment, then dimly. Nothing ever comes on the screen. Yet, the DevTerm works just fine plugged in.
how do you know they are fully charged? If they are Li-Ion batteries they should be empty at around 3.7V, if full they should be at 4.2V, at least mine are… So if you have charged them full with an external charger and they show 3.9V I think something is wrong with them. Are they Li-Ion or maybe LiFePo? Those are lower voltage and might not work in the DevTerm.
Thank you @stefan. Unfortunately, my problem isn’t with “what batteries to use,” (I have 4 that fit fine) but rather that My DevTerm does not OPERATE (turn on, run, whatever) when not plugged in.
Clearly there is something wrong with either how I assembled the DevTerm, with the DevTerm parts themselves, or perhaps my batteries (but having 4 that all work in other contexts seems to indicate the batteries are probably fine).
I was wondering if anyone knew what to look into, or how to get my DevTerm working on batteries. As a wired-only device it is … not particularly useful.
unfortunately that is not so easy.
You told us your batteries measure 3.9V fully charged. That is not normal for Li-Ion batteries when not connected. If they are without load they should be at 4.2V. that is because the voltage will drop as soon as they have to provide power.
If your batteries have only 3.9V they are either not Li-Ion (for example LiFePo) and therefore likely not compatible since the voltage drop under load will drop below what the DevTerm needs or if they are Li-Ion they are worn out. The test with your flashlight is not really helpful since the light will work with lower voltage, the DevTerm will not. Try new batteries that measure 4.2V fully charged witjout load.
Hooe that helps…
thats due to how batteries work, 3.7 is the nominal voltage. The voltage is a function of the stored energy and the load. If you measure 3.7V without load it should be empty. If you measure 4.2V and then add a load the measured voltage will drop.
Please be careful with Li-Ion batteries, they can be dangerous if handled wrong!
When I saw you mention 3.9V full charge I was also suspicious about the health of the batteries, at full charge they should be 4.2V.
Its always a good thing to test them but not everyone has the means to do so.
I was experiencing percentage drops and sometime brownouts. Then I measured my batteries which are rated 2200 mAh and one of the cells reports around 1000 and the other 2200. Even thought they are bough as a pair, prepacked from manufacturer. So that explains why I have sudden drops in percentage, one of the cells is just bad and doesn´t have the capacity it claims.
So, after fully charging my batteries, I left the DevTerm on to run at idle. The only thing it was doing aside from sitting at the logged-in GUI was running an SSH session where I was polling the battery every minute. It took 70 minutes to go from “full” (which was 96 then 90%) to powering itself off.
Clearly, it would seem, the 18650 batteries are adequate for flashlights and grossly inadequate for DevTerm. After the DevTerm shut off, the batteries read 3.85V unloaded. So, from 4.15V to 3.85V at virtually no load in 70 minutes. Seriously doubt these are 3000mAh batteries. I guess I will look at the other thread and find good batteries.