Updated July 2025

AC Coupled or DC Coupled?
You may have heard the terms but not really known what it means so let's go !
When you buy ANY home storage battery, AC or DC Coupled, you are getting...

An inverter
The battery
One 'smart meter' for DC Coupled or two 'smart meters' for AC Coupled.

The smart meter is installed in the switchboard with clamps around the house main supply cable(s).
It measures all the power use in the house and tells the inverter when to release battery power.
With AC Coupled batteries, a second meter is needed to measure the production of the existing solar inverter.
It is therefore, because of the extra 'smart meter' more expensive to go 'AC Coupled'.

How much does a battery cost?
Let's look at some DC Coupled battery examples.

Growatt MIN-XH2 5kW 1ph inverter, 1 phase meter, 13.5kWh (usable) battery, $14,365 installed.
Deduct $1,300 for the WA battery rebate and $4,375 for the Federal subsidy and that leaves $10,025 to pay.

Growatt is a budget brand so let's look at something a lot better...

Sigenergy 5kW 1ph inverter, meter, 15.6kWh (usable) battery, $16,400 installed.
Deduct $1,300 for the WA battery rebate and $5,075 for the Federal subsidy leaving $7,275 to pay.

What features are inside each battery?
Most batteries are lithium iron phosphate (LFP) cells in series-connected stacks.
BYD, Sungrow, Goodwe, SolaX and many others fit that description.

The trouble with series-connected is that all the battery modules are treated as one unit.
All charged and discharged and cell-balanced as a single unit which is inefficient.
Adding a new battery later to an old stack of series connected batteries isn't great either.
Ignoring the hoops the installer has to go through, the reality is the new battery will behave like the old ones.
It will be dragged down to the level of the worst performing battery in the old stack.

So after that lengthy explanation, let's just say that parallel-connected is much better.
Better still having an optimiser or separate BMS inside each battery is better still.
Then each battery is a law unto itself.
Charging, discharging, cell balancing independently.
Kinder to the battery, more energy throughput, longer expected life.

I picked Growatt and Sigenergy in my above example because they are both parallel-connected and optimised.
Sigenergy and another brand called iStore, go one step further.
They have fire extinguishing bags and gases inside.
Multiple temperature sensors detect if a damaged cell is overheating and the extinguisher deploys.
Stops thermal runaway before it can get going.
I'm not saying batteries without fire extinguishers are dangerous.
I'm saying, its an extra feature designed to inspire confidence and peace of mind.

How much can you save from a battery in WA?
Emphasis on the word 'can', not 'will'

Let's run the number on the above Sigenergy 15.6kWh battery.

If you were on the fixed rate A1 tariff then each kWh of battery used in your home saves you 32.3 cents.
Therefore emptied once a night, that's 15.6 * 32.3 cents = $5.03 saved a night or $1,836 a year.

If you were on Synergy Midday Saver tariff there's a bit more guess work required...
Battery power used between 3pm to 9pm is saving 53.8 cents per kWh
After 9pm to 9am the next morning the saving drops to 23.7 cents.
Let's say that 10.6kWh is used during the peak and 5kWh in the off peak.
(10.6 * 53.8)+ (5 * 23.7) = $6.88 a night or $2,511 a year.

In these examples I have ignored the cost, if any, to CHARGE the battery every day.
Most people will charge it from from their solar and for small installs getting the DEBs feed in tariff (FiT),
if that power going into the battery had gone to the grid instead then each kWh was worth 2 cents.
That will change the numbers a bit, but for people with inverters greater than 5kW they don't get a FiT.

Can the battery be drained every night?
Yes, they are designed to be drained from full to zero every night.
Each manufacturer includes a safety buffer of extra storage that you can't access so it's not truly drained.
So if the spec sheet says 100% DOD (depth of discharge) then that's what you can do.
In the Growatt example above I said the battery is 13.5kWh but the spec sheet says 15kWh with 90% DOD.
15 * 90% = 13.5kWh "usable"

How many 'cycles' in the warranty?
One 'cycle' is a discharge to empty from full.
Most manufacturers offer between 6,000 to 8,000 cycles in their warranties.
6,000 cycles, with one cycle per day = 16.4 years and 8,000 cycles is nearly 22 years.
As manufacturers never want to pay out on a warranty they then restrict it to 10 years.
The warranty will say "10 years or 8,000 cycles, whichever comes first".

"Energy throughput" is a much more meaningful metric that 'cycles'.
Sigenergy for example say that their 7.8kWh (usable) battery is warranted for 23.77MWh
That's 23,770 kWh of energy from the battery under their warranty.
If you emptied the 7.8kWh battery every day that's 2,847kWh a year.
23,770 / 2,847 = 8.349 years not 10 years.

Every year batteries release a little less power than they did the year before.
Sigenergy don't want to give you a new battery under warranty so they are being ultra conservative.
I wouldn't like to stick my neck out and say what the total energy throughput over the life of the battery will be,
but I'm pretty sure it's going to be a fair bit longer than the warranty. 😉

Do I get power during a blackout from my battery?
No. You need some extra circuitry for that..contactors, breakers relays.
It's all pretty standard electrical stuff that's needed to 'island' your house from the grid in a blackout.
You need to be 'islanded' so Western Power/SES workers don't get zapped by your battery while fixing the problem.
As Australian residential switchboards don't have the space for all that extra equipment, a separate box is needed.
Often called 'Gateways', these boxes usually cost about $1,500 including installation.
Some can backup everything in the house, others just 'essential loads'.
Some switch over instantly the grid is lost, others take their time.
There are pros and cons for 'instant' or 'delayed' switch over.
'Delayed' let's you know there's a blackout, 'instant' is good for your computers and other sensitive electronics.




This review was written by Andrew MacKeith, Solar4Ever service manager since 2011.