Backup battery Daisy-Chain?

so i picked up a second battery backup unit, as it was on sale yesterday @ newegg for $130
now, for best runtime,

seems like, when my hdds idle down im sitting on 48w tv and 97w desktop

should i split the load between each unit as best i can.
daisy chain the units?

they don't say that they are "daisy-chain-able"

but the units are fully pfc and PURE sine wave compliant.
which in MY MIND reads as.
one should not be able to tell the difference between
the output of A unit and the mains from the wall.

so in that case, why would it matter if one is plugged into the next?

so long as the Total Load is within the units rated outputs.
my max load should never exceed 400 watts.
and these are rated @ 810watts.

I actually had this same idea but using like 5 of those usb battery banks for phones. I don't see a problem with how you have that setup, but I'm no electrician lol.

reading from this other companies thing, the REASONS listed,
dont really conflict with my setup....

If there third point is accurate then you might not see added run time although you could test this. Otherwise, I don't see an you being affected by their other two points.

I wouldn't daisy chain them unless you were sure that the power draw on the UPS while it is charging is within what the first UPS can output.


You'd also want to make sure that the total load of both chargers and everything connected to it doesn't exceed what the power outlet is rated for or what the fuse in the UPS is rated for. Otherwise when power is restored and it tries to pull 3000w or something then something is going to trip out or catch fire.

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If you daisy chain battery backups together, you have twice the load running through both units all the time, rather than half the load between them if you were able to distribute the load evenly between the two.

Splitting the load would most likely increase the life span of both units, daisy chaining might lower the life span. I have had battery backups in my server room with 80+% load die within a year, same model with 30% load has been going 3 years strong.


generally ive found only text that doesn't really apply to my situation

in my case,
ive purchased 2x "GX1325U" sine wave output 1325VA / 810watt "gaming battery backup" units

all the text ive found only states that stacking will not increase battery backup time
because the power from one ups is simulated or stepped and will trip the clean power of the second unit, thus draining both at the same time.

this should not be the case with a "pure sine wave" output unit.
as one unit should be electrically indistinguishable from mains power vs the other battery backup

the only other issues commonly addressed are

stacking the units may "overload" them

in my case,
I am running 810w units with the loads split between both ups,
(desktop on one ups, screen and networking on the second ups)

but my Maximal COMBINED Load never exceeds 310watts
just the rather high efficiency gaming computer and a monitor
(at non gaming idle, this system + screen only consumes 155W)
(in game usage of the desktop is only 310W in worst case loads)

id need to battery operate one ups till it was about half cap,
and stick it onto a Kill A Watt reader to get an idea of the CHARGING power draw

if that charging draw + the load of my setup is within 800Watts then in theory the first ups system from the mains shouldn't complain

my main issue is, im only plugging in 2 items.
the desktop which idles as low as 95w and games up to about 250w
the screen which is a flush 48w at all times.

my goal is to maximize the runtime on Both of these devices
cant really operate one with out the other

yea. im curious as to a graph for this.
i know that the SLOWER we drain the battery the MORE efficient the process will be.

so less load will give More time overall
the more load on the same unit, the lower amount of TOTAL system output you can get from the same battery cells

my main issue is,
ups#1=60w draw
ups#2=95-250w draw
= uneven runtimes between the screen and the desktop
one is getting like up to 5 TIMES the draw as the other if in game
and 2 times draw if idling or movie watching

Do you know if these units constantly run the inverter all the time, or switch to inverter when you loose mains power?

If this is the case (which it is with many commercial backups), you will want to count in about 10 to 20 % loss. But even with this loss between both UPSs, you will be fine. These modern DC charging circuits are fairly efficient, so you should not loose much to the charging circuit.

If you have a Kill-a-watt, this would be worth testing. You will probably have no more than 600 watts measured at the wall at load, with the draw from the backups included.

they are line interactive,
so they kick within a second of power irregularity into the battery inverted mode.
CyberPower GX1325U 1325 VA 810 Watts 10 Outlets UPS
ill give em a test on the kill a watt, suppose the easier way will just be to unplug one for a few minutes lol

i am seeing anywhere from 10 to 15- 20 watts At the wall vs whats displayed on the ups

this ones @ 20w difference

its also looking like, on the unit that just has the a399u screen,
estimate run-times are 70 minutes or so.
ill run it down to 50% and then plug that into the killawatt
and see the charging draw


You need to include the load of the UPS charging its battery. Its more than likely that the charger is using 10amps or something like that. It will probably say on the back of the UPS. You need to consider the load of both chargers and the load of everything you have connected.

ok charge testing done

it looks like, with ZERO load.
the AT-wall draw for recharging is a WHOPPING 21.7 watts

WITH the screen on and drawing its 48W
AND charging the battery back up the draw is DUN DUN DUN
73 Watts

73 watts minus 48 watts iiiissss = 25 charging watts

at WORST CASE. im talking MAYBE 320 watts for the desktop AND screen.
PLUS say 60 Watts for BOTH ups' chargers combined.

TOTALLING @ less than 400 Watts AT THE WALL draw.
IF i were in a game at that time.

even worst case, taking into acct EVERYTHING.
the Draw is still HALF that of a SINGLE ups unit's RATED output.

So this sorta kills that other reason.
It won't 'overload' the first unit.

It's supposedly pure sine wave.
Meant for use with "sensitive" computer equipment that has active PFC.
So one unit should not see power from the other as 'dirty or bad'
@wendell hows you electrical engineering these days?

Ok, so the last thing I've read, that would stop me.
Is this page talking about the voltage/surge resistors

It claims, plugging the ups into a surge protector.
Can screw with the electronic signal. And reduce the ability to clean the power.

Wouldn't I WANT the ups in series?
Say lightning zaps my home.

Mondo power surge.
Fries one unit.
The unit does its job. And sacrifices itself to save what's plugged into it.
The second unit kicks to battery and I keep on playing.


Have the two plugged to individual wall sockets directly.
as suggested by the manufacturer.

Lightning hits.
Both units die.
And I loose power to my system.

I'm a schooled engineer...

What is all this silliness about "pure sine wave"?!?! All AC power alternates as a sine wave. Lol.

Yes, you can just plug one into the other so that it's like one is charging from the other. However....

  • it's not super efficient
  • you cannot pull more load than a single one can handle
  • the behavior could get weird as they begin to discharge under heavy load.

It would be safe to try it but maybe try with a few 100watt light bulbs first. Try a single, measure the time it takes to discharge. Then, charge it back up and add one. Measure the time again and be careful to observe which one drains first etc. See if anything weird happens. It won't damage them .

I think you will find using two will get you about 1.8x, not quiet double.

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I wonder if the control boards could handle it if you just wired both sets of batteries into the same UPS.

Though, I would consider making a power Y adapter that takes all your components and allow you to plug into both of them at the same time.

would you call 40% rated load

you know. tha'd probably be the easiest method
i wonder if it would piss off the inverter over the longer duration
then again, if it will run over an hour with just the screen.
i dont see why it cant run longer..

would adding more sets of batteries in parallel increase the "stress" / heat. of the inverter section ?


70%-90% - heavy
>90% - what are you doing?