I found a supplier for a 500 W, 12 VDC to DC converter, where you can select the output voltages: 24, 30, 36, 40 and 48 by setting DIP switches. I have ordered one for myself to test it. Since I am seeing this as new, I can only suggest this to anyone who wishes to change their Bluetti battery from the 12 VDC auto supply through the PV port at a higher voltage. It is just a board and need a case and cabling, so it is a DIY device, not for those who just want a ready to plug in device. Its regular price is $55.99 but the special price is $23.96 plus shipping (you select it at checkout). Payment can be done through PayPal.
Here is the web page for the converter:
WONDOM | STORE
Please post if you placed an order so I know who ordered it. Then we should return and post here the result so others can decide if they wish to buy it.
As I wrote above, this is a suggestion and I am not responsible if it does not work for your need. It was developed for car audio specialists who need higher voltages for special high power amplifiers, which are also sold here. This web site has other items for DIYers in audio and other devices. Just look around.