Owon HDS272S "Low Battery" at 3.7V, switch-off at 3.5V...?!?

[lvml]

Hi, in terms of functionality I really like my recently bought Owon HDS272S a lot - but I came across a very strange issue with its "low battery" detection: The battery indicator changes from "half full" to "red/empty" abruptly at pretty exactly 3.7V battery voltage - and the device switches off when the battery voltage has reached 3.5V.   

This lets about half of the energy content of the battery unused - while of course ending operations on battery unfavorably soon.

I checked the capacity and impedance of both 18650 cells - those are fine - their capacity is even somewhat better than advertised.

I also powered the Owon HDS272S from a lab power supply, this reproduced the behaviour with the battery perfectly, so the issue has to be with the detection of what is considered "low battery".

Has anyone else experienced this issue?
I wonder whether I should return my exemplar as faulty, given that half the possible battery life is kind of disappointing.

(It's nice, though, that one can power the device from USB without batteries in it, for stationary use.)

[Fungus]

Hi, in terms of functionality I really like my recently bought Owon HDS272S a lot - but I came across a very strange issue with its "low battery" detection: The battery indicator changes from "half full" to "red/empty" abruptly at pretty exactly 3.7V battery voltage - and the device switches off when the battery voltage has reached 3.5V.   

3.5V seems like a reasonable cutoff voltage to me.

This lets about half of the energy content of the battery unused

I doubt it on a low-load application like this (it goes for several hours, right?)

The way to check is to measure the battery voltage after you switch it off. If it doesn't bounce back to much above 3.6V then there's nothing left.

[J-R]

While there is some variance due to chemistries and manufacturers, most Lithium Ion cells are basically dead at 3.5V.  Discharging this low reduces the battery's life, so it would be better to charge it back up before dropping below 3.7V.

[dophuc]

This is completely normal for many devices that use lithium batteries. Manufacturer setting cutoff to protect and prolong lithium battery life. The deeper the lithium battery discharges, the shorter its lifespan. I also use HDS242 and the solution is to prepare several pairs of 18650 batteries to replace when the battery is low 

[lvml]

Hmmm, I'm all for keeping the batteries alive, but AFAIK leaving 15% of the remaining energy in them is sufficient for that.

Looking at typical discharge diagrams - https://lygte-info.dk/pic/Batteries2012/common/MediumCapacity-0.5.png for example - a "low battery" warning at 3.7V means that you are somewhere between 50% to 70% remaining energy when the warning is displayed.

The switch-off at 3.5V may be ok, but the warning - which is displayed mid-screen in oscilloscope mode - is annoyingly early.

[Fungus]

Looking at typical discharge diagrams - https://lygte-info.dk/pic/Batteries2012/common/MediumCapacity-0.5.png for example - a "low battery" warning at 3.7V means that you are somewhere between 50% to 70% remaining energy when the warning is displayed.

Nope.

The measured voltage will depend on the battery capacity and the load on the battery at the time. Those curves show battery voltage for a 2600mAh battery (approx) which is loaded at 0.5 Amps.

Those curves are only applicable if your battery capacity is similar and your gadget is drawing 0.5 Amps.

(This effect is due to "ESR" if you want to go and read about it)

[Ice-Tea]

Visual to Fungus' remark:



So, yeah, at low discharge rates 3.7V *is* low battery.

[Fungus]

Visual to Fungus' remark:

So, yeah, at low discharge rates 3.7V *is* low battery.

The Owon claims 6 hours battery life so that's 0.16C

That means "low battery" is where I've put the blue cross and "dead" is where I've put the red cross. Both seem bang on to me.

[Flopdoodley]

A few months ago Owon revised the 6-hour battery life claim to "for about 4-hours" as described on their product page and the user manual.

https://www.owon.com.hk/products_owon_hds200_series_digital_oscilloscope   (referenced three times on this page)

http://files.owon.com.cn/probook/HDS200_series_user_manual.pdf   (see page 40)

[miklas]

The OP is right. How about taking out batteries when Owon says "low", and still manage to pull out 5Wh of each cell? Magic?