What I’m trying to figure out now does it provide “Regulated” 12v? If the battery voltage varies as it draws down or charges, will the D40 output exactly 12v no matter what? I have electrics that I want to connect to the DC circuit powered by the D40. It has to be 12v all the time.
Do I have to buy a DC regulator to make sure my voltage output stays at 12v?
The D40 primarily is a house battery charger from the AC200L’s 30A output port. Batteries all charge in excess of 12VDC, i.e. up to and slightly higher than 14VDC depending on chemistry.
Lead Acid batteries all output in excess of 12V i.e. a full AGM sits at around 12.8VDC and reduces as the battery is depleting. LFP is more constant and sits at around 13.1 to 13.2V for most of it’s cycle.
This also applies to vehicle powered devices as the alternator voltage is also above a nominal 12V. Most devices will have a working voltage range, many of up to 15V, to cater for simultaneous charge discharge voltages.
The D40 has a supply mode, but the user manual only specifies 12V as a nominal output, it may be slightly higher, it may fluctuate, only Bluetti can answer your enquiry.
I would edit your Q to start with @BLUETTI_CARE this will tag the Q directly to Bluetti Support. I would also suggest that you specify what it is you are requiring a fixed maximum to power, of 12.0VDC, for a more informed response. 
Hi @cliffrodriguez, Thank you for your attention to this issue.
@Mandp’s explanation is very accurate and comprehensive. The D40 is compatible with diverse battery types, including LiFePO₄, AGM / gel, lead-acid, and calcium batteries.
When the D40 supplies power to the DC battery via the AC200L, it will automatically adjust the output voltage according to different batteries. In load mode, the output voltage of the D40 is around 13V, so you can use it with complete confidence. There is no need to purchase a DC regulator.