question

80V is a non-standard ssytem Voltage for battery inverters in this market. In this industry, the standard Voltages are 12V, 24V and 48V based on readily available 12V lead acid batteries.
Building an 80V model would not make much sense because of low demand.
Agreed, a higher Voltage design would be more efficient due to lower current throught the bridge and sense resistors etc. but not really high demand for non standard operating Voltage.

A wide range input design would be very expensive too, the MOSFETs in the bridge would need to be huge to be able to carry very hifgh current if used with lower Voltages and also have high breakdown Voltage if used with a higher Voltage. Either a great many high Voltage MOSFETs in parallel or a few very expensive high Voltage / high currrent types.
Also the DAC would need to be very high resolution in order to produce a faithful sine wave across the entire input Voltage range.
The transformer primary would need to be wound to carry the highest current in case the unit is used with a low input Voltage, wasted resources if the unit is used with high Voltage.
Much better to build inverter with a specific narrow Voltage range in mind. The transformer winding can more closely match the expected input Voltage and the PWM can be kept at a reasonable 10bit resolution and maintain a faithful sine wave.

The other issue is safety regulations; IIRC voltages higher than 60V maximum are no longer classed as "low voltage" and this has many implications for components, wiring, insulation, testing and maintenance.

So once above 48V/50V systems there tends to be a big jump to 400V or so which is no worse for safety but has far thinner/cheaper wiring/switches/connectors and is common with EVs and high-power industrial installations -- the semiconductor switching technology is also cheaper and more efficient.

80 is absolutely standard system voltage for all bigger forklifts and similar vehicles.

See the 24/48/80 Volt models composed from 2V lead acid here: https://www.staplerbatterie24.de/

All forklift manufacturers manage the safety regulations for this voltage although it may reach 94V temporarily for charging up to 2,35V/Cell. Cable, connectors, fuses are all same than in 48V systems. We have 3 forklifts with 80V in use and total capacity is >>100kW hours why its a pity we cannot connect to ESS.

The disassembly of my multiplus shows a torroid transformer with 4 parallel copper wires probably to improve skin effect and ease the manufacturing process by more flexible wires. I could easily change transformer ratio using 2 windings in serial to match the 80V approximately. N-channel Mosfets shown great improvements in the last years and for higher voltages low-Rds-On is available. Used capacitors should have double voltage and may be dropped in capacity for same size. Further we have to increase any resistors in sensing voltage divider to make the software calculating with 48V levels. This way modification should work without affecting any firmware and if I drop the DC power supply it should mainly work. Up on now, I did not find any pcb schematics and board assembly drawing to navigate in the circuit more easy.

If there is no support for such modification we do have the 3 phase chargers for 80V systems suppled with the forklifts. It could be feasable to connect the 80V level to additional 48V battery by use of a MPPT 150/100. This could discharge a 50KW/h 80V battery with about 5 kW in around 10 hours thereby supporting the 48V system. I assume the MPPT use non isolated buck regulator circuit instead the toroid transformer in my Multiplus. Here I do not understand the reason for the value of "maximum panel short circuit current" (what is not only given for Victron MPPTs).

Lead acid cell resistance is expected much smaller than PV module why probably the MPPT functionality does not make any big benefits. If the MPPT algorithm is searching down to smaller voltages assuming further maximums there, it should stop before destroying itself. If MPPT cannot deal with low impedance sources (for whatever reasons?) any PWM light charger should do the job and only disadvantage seems the 30 Amp limit. What are other pitfalls or suggestions doing this ?