Hi Dave. @dnknecht I decided to install 35v (because it will be more longer to die) but it’s my theory. Now I have your proof. Thanks for your comment! 
Regarding soldering: So you didn’t removed old one cap’s legs and just cut the legs 
so in such case I don’t need to dissasemble all 100500 wiring harness and electronic board itself. Do I need to make the new cap legs shorter? Or cap legs length is not a case? I’m a newbie in such things like capacitors 
Dear community, my SOC is dropping zero for a couple of minutes (see the screenshot). But grid is stable and connected! I teared down my AC300 and capacitor was bad (same as on the picture in previous post)
The interesting thing- I have another AC300 new (capacitor is good!) but problem the same!!! What a h…! Batteries are good
FW is not a case (2 AC300 has different fw)
@BLUETTI_CARE hope you have some idea
Hi @Arvian, according to your feedback about the faulty capacitor and error code 006, please troubleshoot step by step as follows.
Please disconnect all loads and restart the unit. Did this help?
If the error still occurs under no-load condition, a repair will need to be arranged.
If you have any questions about how to reach the appropriate customer service team or concerns about the service process, please send us a private message with your order information so that we can arrange priority service for you.
The capacitor has white silicone around it’s base. Use an Exacto blade to cut the silicone and then you can twist the cap back and forth until the cap detaches from it’s legs. I soldered the new cap to the old legs. One leg was longer on the new cap, so I cut it off to match the other. The longer legs don’t cause a problem, since there is lots of room above this part of the circuit board.
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Thanks so much Dave! Everything clear. Much appreciated.
Dear Community, I confirm that changing capacitor from the pic @Haolemon - helped! 006 problem solved 
In my case it became from daily (I mean error 006) to every minute! Capacitor was swollen.
I changed into original Panasonic EEUFS1V102L (fs series because it’s narrow) 35 volts (you will receive 10000h instead of 2000h in original 25v Bluetti cap). More volts more ripple current (but 35v max ;)
Thanks so much @StingerZ16 for this thread and @Tpochowicz @Haolemon @dnknecht for your input!!! You are amazing!!!