question

to expand on @WKirby above.

I had a quick look at Victron site and [see reply below] the 48 V 500 VA MultiPlus. As WKirby says 500 VA is 'small'. From the spec the charger is 6 A (@ 48V).

We have a MultiPlus 24/5000 (VA) /120-100 connected to two Victron 24/200 AH LiPo. And sizing size the generator is a balance. In our case the 'charger' side of the Multi can only deliver 100 A at 24 volts. So regardless of the size of the generator that is the maximum - in our case 4.5 kVA generator has some 1,000 watts in excess which we use on 'pass-through' to heat water at the same time as well as microwave, etc.

The recommended charge rate by Victron for our batteries is <=100 A / battery = 200 Amps continuous charge. Going higher than the recommended will have an impact on the battery life (negatively). Correct cable sizing etc.

Your 2 x 48 v LiPo I would imagine could handle anywhere up to around 200 Amp (each) but to get a generator to deliver that you will also need a charger than can delivery. Furthermore the capacity of the generator (continuous output power) is less than the nominated maximum and you will need some 'excess' (head room) in order to avoid getting distortion to the waveform which the MultiPlus might then reject.

As your charger is actually 6 Amps, WKirby points out you will be spending a lot of time on fuel to get 48 V 100 AH up to 95% from say, 50%. See recommendations on SoC for long term life of Lithium (i.e. do not fully charge regularly and perhaps use between 90 - 50% SoC - your research required here).

In our case we get around about 1% SoC increase for every 2:25 minutes (say 2.4 min) at 100 Amps charge at 24 volts. For you being at 6 A vs 100 A you will need 38 min / 1% SoC increase. Say [(95%-50% = 45% SoC] * 38.4 min/% increase = 38.4 min*45% inc = 28.8 hours. Generator at say, 1.8 l/hr at 6 Amps = $1.60 / ltr * 1.8 = $80-85. You might find that an analysis of the frequency that you need to run the generator connected to your current charger vs spending less on fuel and getting a larger charger is worth a look.

You state above that the load is only 70 watts (@48 v = 1.45 Amp) but I have no idea of your latitude (solar yield) then with 1kVA solar you will likely never likely need a generator in any case. If my assumptions are anywhere near correct you could just get a portable 'Honda' 2kVA petrol generator to get you out of a jam because anything 'industrial' will likely be a 'mismatch' with your charger and will require a lot of $'s. Your comment about generator being outdoors is 'missed' on me - for what reason other than common sense because they produce dangerous vapours which can kill quickly- is there another reason you mention this? Petrol generators outdoors in rain will also kill quickly unless you are very (very) prudent - not recommended by me so hence your reason for 'industrial' (meaning diesel??). Best wishes on getting that resolved satisfactorily.

A few things to keep in mind,

I doubt you'll find any "industrial" AC generator that'll run effectively at that low of a draw (if it is indeed 500VA). That kind of draw is more appropriate for one of those Honda "suitcase" generators. The smallest they make is a 1000W. It sips fuel, can have an "extended run" fuel cap added, that allows the main tank to draw from an aux tank. It's not auto/remote start, it's pull start, but that's about as much generator as you should run for that kind of demand.

Which leads to the next point, you really should not run a generator (especially a diesel, which you're most likely going to find in the "industrial" range) below 50% load.

Ideally generators do best within 60-75% loaded. A lot of people overbuy a generator, end up running it at 10-20% load and eventually kill it. Not to mention that fuel to watts ratio is way better, the faster that little motor is spinning (within its powerband of course) the more efficient it is.

My onan takes .5 gallon of fuel to produce 3000W, .9 to produce its full rated 7500W, and .20 just to idle and do diddly.

My Honda may run for 8.5 hours on a tank of gas, and produce ~3650W, but can produce 5760W running at its rated load.

If you *have* to underload a genset, gas is more tolerant (slightly) than diesel or LP, but it's still not a good thing to run it for hours upon hours underloaded.

This is the main reason I love lithium. We fire up the genset, dump 105A @24V into our batteries. We're in for an hour and some change (depending on SOC), heat water, cook, and other high loads, run the genny at 60-70% for the majority of it, and we're done.

There is an even smaller Honda generator which I highly recommend: EX7 it is called.

It is mostly overlooked because it is not an inverter but a cyclo converter with a tiny 600W rating. However it is marked less noisy under full load than the small inverter probably because of lower rpm (which it holds at all times so no down idling), it takes less fuel per hour under full load at 0.47 l/h near the 600W feeding my Multi 24 3000 70 set to 18A compared to sources where the inverter was tested ar slightly higher loads, and cost 65% of the 1kW inverter. I think its the same engine, regardless it starts like only a Honda does.