Freshman, as has been already stated you need to do some homework and calculate your
current needs and also your planned needs. Add to this your
safety margin and then total capacity (over say 3-4 days/0.6 (60%) of your needs to determine your total house-bank capacity. i.e. you should never run your Lead acid (of any kind) down below 60% (trouble starts at 80% for 'flooded types') AND they (house
battery types) do not like high-current draws (i.e. the coffee maker; aircon etc) even if there is an
inverter that will deliver it. Equally they (Lead acid) do not respond well if never fully re-charged. To this end it is my understanding you LA
battery cannot (does not like) 'high current'
charging in any case regardless of whether your new alternators can deliver it (will cook them - acid stratification or sulfation for proper terms - see good websites for how to look after your LA batteries). One reference which is I find helpful
Absorbent Glass Mat (AGM) Battery Information - Battery University
Your investigation may therefore take you to new battery technology (i.e. Li) as this does accept high charge rates (and reduces weight for same VA.
Based on our needs (incl contingency) we installed a water-cooled 4.5 kVA generator. This is a
Northern Lights unit which at the time (five months ago) was the 'smallest' capacity generator that ran at 1,500
RPM to make it 'tolerably' silent (water cooled) - we do not actually need 4.5 kVA. We use this for 240 AC supply for tools, coffee maker, microwave, (all high
current devices). We have 1 kW
solar (latest generation so optimal production for low
solar angle and partial panel shading issues); and even after several days of rain or poor solar radiation we have not needed the generator solely for
charging the
batteries. We
motor sail reasonably regularly or when repositioning - regularly not less than weekly and with 60 AH alternators on each
engine and cannot 'use' all their output in any case; we rarely visit marina's (shore power) so solar is needed 'every day' to take the LA
batteries (AGM type) back up to full
power (i.e. 'float' for hours is needed). Our NL generator only uses just over 1.2 l/hour when running (1.9l/hr full load = 4.5 kVA is never achieved even when we heat our 60 litres hot-water to make the most of the generator capacity as the 'element' is limit to 750 watts so that
shore power (220 V / 15A) regulated) is not exceeded assuming that other 'loads' will be present together with the
water heater when connecting to
shore power. Again this is only practically whenever the real-coffee caffeine-low light comes on (say every 3rd day) or we are hosting guests with increased
water (fresh water generator)
shower usage; lights,
equipment recharging etc;
cooking (microwave, cake mixer; more frequent fridge opening etc. is required. The 'cost' was not really justified given that we have two engines each with alternators but I did not want to run a 75 hp
engine (much higher
fuel consumption and absolutely hates being idled for hours without 'real' load) to generate
power. Also got rid of our 2KVA (= 8-9 amps) portable unit as this was unable to run power tools (e.g. portable grinder, coffee maker, aircon etc. and with it sitting out on the rear
deck it was noisy (all the time) and in the rain (when often needed to recharge batteries before new solar) it was downright dangerous.
Hope this helps.