this is getting very interesting!
My cyberpower ups is in a metal case..not plastic...and can use an internal 48 volt battery pack...however I do not use it....there is no protection, fuse or otherwise, from the battery pack to the ups.
my ups can use up to 6 external battery packs in metal cases, connected in series. output of each case has a circuit breaker and each internal string of 4 9ah is also fused. each case will hold 2 of these 48 volt packs and each case is equipped with its own battery charger. as can be surmised, these cases are heavy with fully loaded!
since I currently use just two of these cases I don't use the internal chargers.
each case has provisions for 120 vac inputs.
Ok , good info.
I would say that you would be fine to connect it to whatever capacity battery bank you wanted, as long as you didn't exceed the float current required by the battery plant.
The packs are internally fused I would guess creating a safety for shorts and the like. Typically they are in line of the batteries somewhere. APC likey to put them between the center of the battery string. But I am betting it is somewhere within the packs.
And while the packs connect in 'series' understand that it's still 48 volts so teh packs are in parallel, maintaining the 48 volts to the unit. I assume they just daisy chain together.
Yes, I bet those are some heavy packs. Four 9Ah batteries is gonna have some weight to it.
My big UPS (18Kva) is a bit different in that it runs 2 72 volt trays in series per level and has 5 levels and has a battery cabinet that will parallel with it that contains another 8 levels. Of course I am not running any of the batteries that came with the unit because the dumb thing needs 60 7Ah 12 volt batteries to fill all the trays and I am NOT gonna spend that sort of money when I have a source of 75Ah batteries I can use.