How Hard Should You Push Your Home Battery?
One of the most common questions I get is not about how Powston trades, but how hard it should trade.
- Is a 5 c arbitrage worth it?
- What does a battery really cost per kWh?
- Do you use the sticker price, the post-rebate price, or something else entirely?
- Should you be thinking about lithium prices five or ten years from now?
- Do you want a lower bill today, or a battery that lasts a few extra years?
They are all good questions. And they all matter.
The Hidden Question Behind Arbitrage
When people ask “is 5 c arbitrage worth it?”, what they are really asking is:
Am I trading battery life for short-term savings?
To answer that, you first have to decide how you value your battery.
Some people think in capital cost per kWh.
Some think in cycles remaining under warranty.
Some think in total household bill reduction over time.
There is no single correct answer.
What Does Your Battery Actually Cost?
Battery cost is not as simple as the invoice number.
- Do you include the government rebate?
- Do you amortise over the warranty period?
- Do you assume the battery lasts longer than the warranty?
- Do you expect lithium costs to fall in 5–10 years?
If you assume:
- A post-rebate installed cost
- A warranty-defined energy throughput
- And no residual value beyond warranty
You end up with a conservative “cost per kWh moved”.
But many users do not think that way at all. They think in terms of cashflow. Lower bill now, worry about replacement later.
Neither approach is wrong.
Warranty vs Battery Life vs Use-It-Or-Lose-It
This came up in a really good Discord discussion recently.
There are two schools of thought:
1. Use it or lose it
- Batteries degrade with time regardless
- Cycling within warranty is what you paid for
- Savings now are certain, future battery value is not
2. Preserve it
- Gentler cycling may extend usable life
- Less degradation means more optionality later
- A battery that still works in 12 years has value
Both views are rational.
Where I Personally Land (For Now)
Right now, I tend to anchor to the warranty.
I am comfortable cycling the battery in a way that broadly uses up its warranted throughput over the warranty period. After that point, the goal shifts almost entirely to bill reduction and risk management rather than preservation.
That means:
- I am okay with relatively small spreads if they are frequent and predictable
- I still avoid pathological cycling that adds wear without value
- I reserve headroom for high-value events rather than chasing every cent
This is not a permanent position. It is a practical one.
Import Factor: Letting Users Choose
Because reasonable people disagree on this, Powston should not hard-code a single philosophy.
That is why I am working on an import factor that lets users dial this behaviour up or down:
- Push harder for short-term bill reduction
- Or trade more conservatively for longevity
This is not about right or wrong. It is about aligning the system with how you value your battery.
The Honest Answer
The jury is still out.
Battery chemistry, pricing, and market conditions are all evolving. What made sense three years ago is not guaranteed to make sense five years from now.
What I can say with confidence is this:
- These are the right questions to be asking
- There is no universal optimum
- And any system that pretends there is, is oversimplifying reality
Powston’s job is not to decide for you.
It is to make the trade-offs visible, adjustable, and grounded in data.
That is the direction we are heading.