It has been suggested but i have not tried it. I can see how it should work, and it likely will work but it's not a long term permanent solution obviously. Not gonna keep 1000lbs of batteries under my house just so i can use them to help jump start my inverter for the lithiums every time i do a system shutdown/startup.
Not as a permanent solution, but as a test to see if lithium can supply the inverter, even though they have trouble precharging it.
If the inverter could have its capacitors precharged and sit there not drawing any power beyond a few watts for its microprocessor, or even if it started up and drew idle current of 25 or 50 watts generating A/C but loads were disconnected, should be possible to precharge through a resistor, then close switch.
50V 50W is about 1A.
1A through a 1 ohms resistor is 1W steady-state.
50V / 1 ohms is 50A
50V x 50A = 2500W (pulse during precharge)
Some resistors would pop with such a surge, while others could take it. Look for "pulse rated".
A suitable resistor could precharge and power up the inverter so long as loads disconnected, allowing you unlimited time to close switch.
Lead-acid alternative, four small 12V gel-cells might be 50 lbs or less. Series for precharge, rewired in parallel they could serve as a jumpstarter.
Another precharge test: Just use the lithium batteries, but higher resistance wire. Did you make it nice and short? Try a long pair of jumper cables. That could carry full current for a limited time. Jumper cables across switch/breaker, then close switch.
For higher resistance but limited current handling, a 250' roll of 12 awg Romex. Connect white and black together at far end. Use briefly to precharge.
I'm gonna see if i can rig up a 48 volt load like you suggested and see what happens with the battery when i just try to power a simple 48v load.
Yes, this should show if BMS or fuse is dead.