Eddie1

Sure thing
Once I collect enough readings in different scenarios I'll post here

Now I'm sad
I've noticed this too But I thought the problem was the multimeter
But now that I think about it, it's clear that it's not the multimeter but the inverter
There is "almost always" a 0.2v difference (inverter showing lower voltage) even without battery charging or discharging (load using solar) 
My old vm  II 2.5k didn't have this issue. Its reading were accurate and showed any voltage change instantly. it doesn't have any delay while the vm IIII 4k twin has 1 or 2 sec delay when showing the voltage 

push buttons, brand: renovo, my inverter is exactly like the picture I uploaded before
still searching for it, do you recommend some shop?

my original factory firmware is dsp: 71.01 mcu: 57.09
they did send me an ftp link that contained only the files I uploaded here.
I still haven't updated my firmware because the connecter on the old laptop I have, turned out to be VGA and not rs-232 🤣
since we both seem to be from that same country
where did you get the rs-232 to usb cable to update the firmware? I still can't find one to update my firmware.

MCU firmware were never updatable via USB, as of now at least! You must use a USB to RS232 converter to update your MCU firmware.
However, it is possible to update DSP firmware via a USB cable with selecting the "USB" port option in the reflash tool, which is already documented in @Coulomb's firmware update instructions. It is also possible to update DSP via USB OTG, and of course USB to RS232.

just to make sure I understand correctly,
can I update both dsp and mcu on battery only without ac connected? because ac is not stable and gets cut randomly.

I emailed voltronic and they sent me the latest frimware for my inverter
my inverter is renovo vm3 4k twin
current fw is 71.01 and the one they sent is 71.03
as it has been stated before the first number seems to have nothing to do with fw version or date, it might be an identifer for the brand selling the inverter.
if that is indeed correct, I wonder if the inverters have some differences in components for each brand
because why would they send @Mohammad Jawish a frimware with v 60.10 (triple-a brand I presume?) and send me one with v 71.03 (renovo brand)

do you @Coulomb think this is possible? or the components of the inverter are always the same? I have no expertise in these things
but they also sent Mohammad Jawish a copy of v 84.00 which would mean the first number is not a number for a certain brand or at least that the frimwares are interchangable between brands.
 

VM TWIN DSP_7103.7z Remote Panel_Reflash_MCU(5716).7z

Yes.
Wow. Usually Voltronic won't respond at all to mere owners.
Groan. Yet another overlapping firmware series. But thanks for posting the firmwares. I have not seen any 71.xx for this model, and 57.16 seems more recent than version 57.11 that I have.
The first TWO digits are supposed to be unique to a model, but they have basically run out of combinations of two digits, and/or are too lazy to check if the combination is used before.
Unfortunately, 71.xx is used by several other models: Axpert MKS III (not the same as a VM III), Axpert MKS II (with xx large, > 70), and Axpert King 1 (before they overflowed 71.xx and went to 72.xx). I have no idea so far what the difference is between this 71.xx and the 60.xx and 84.00 (and maybe other 84.xx).
There could be differences. Some brands (e.g. Aerox) seem to have an arrangement with Voltronic whereby they get a special display with unique icons, a special power rating (often 200 W higher than other similar models), and possibly other changes. So I would be very reluctant to mix 71.xx with anything else, at least until we know more.
Unfortunately, comparing binary firmwares is a tedious and time consuming business, and I have several other distractions at present.
84.00 seems to be a one-off; I've not heard of other 84.xx. But there could be more. I haven't had the time to compare 84.00 with any of the 60.xx yet either.

Short answer: no.
You need a 128-bit password (32 hex characters), plus special hardware and software, though the software often comes with the hardware, and it's not particularly expensive. But without the password, it simply won't work.
The best that you can do is to find the firmware update file for your existing firmware, or failing that, the closest one to that.

Thanks for your reply 
 
I upgrade my inverter to the mentioned version 
The twin problem not solved 
I faced other problem after the update 
Max charging current reduced to 10amp
I tried to modify it many times but it return to 10amp after battery fully charged and not goes up again.
 
The voltronicpower.com replied to my question about twin problem and send me a special version @Coulomb
 
Dear Mohammad,
 
 
 
Thanks for your e-mail.
 
 
 
The PV energy is not stable, if the 2nd output is turned ON too fast then the 2nd output may be ON/OFF frequently when the PV energy is not stable. We have one special version of Main CPU firmware to turn ON the 2nd output when the inverter backs to AC mode for more than 1 min. Please upgrade the firmware to check if it could comply your request.
 
 
 
https://ftps.voltronic.com.tw/T/Temp-987EB17E23484B20A6C2/VM TWIN_84.00.7z
Since this is the customized firmware and the firmware version is different.
 
 
 
If you want to recover the main CPU firmware back to mass production version, you could also get the firmware 60.10 through below link.
 
 
 
https://ftps.voltronic.com.tw/T/Temp-987EB17E23484B20A6C2/VM III TWIN_60.10.7z
 
 
 
Best Regards,