Your home battery was installed with a minimum reserve level set by your installer. Most battery owners have never changed it, looked at it, or been told what it means for their electricity bill. For many, the adult is costing money it doesn’t need to.
What the minimum reserve level actually controls
Your battery has a programmable floor below which it will not discharge under normal operating conditions. A battery set to 20% will run down to 20% capacity during daily use and hold the remainder in reserve. That reserved capacity sits available for blackouts: if the grid goes down, the battery draws on it to keep essential appliances running.
The financial trade-off is direct. A higher reserve means more blackout protection and less daily use. A lower reserve means the battery works harder every day and earns a better financial return, but leaves less capacity available if the grid fails. Routinely cycling below 20% also increases wear on the battery cells over time, which affects total capacity across the battery’s lifespan.
The right number sits somewhere between those two pressures. Where exactly depends on your household.
What the default is probably costing you
Most installers set the minimum reserve at 20-30% as a conservative starting point. That may be appropriate for some households. For others, it represents a permanent reduction in the battery’s financial output that was never consciously chosen.
A 10 kWh battery with a 30% reserve has 7kWh available for daily use. The same battery with a 10% reserve has 9 kWh available. That is 28% more usable capacity from the same hardware.
At current peak electricity rates of 30-37 cents per kWh across most states, 2 extra kWh of battery discharge per evening rather than grid imports saves roughly $255 per year. Over a 10-year battery lifespan, that is $2,550 in avoided electricity costs from adjusting one setting.
For an inner-city household on a stable grid that has experienced one short outage in 5 years, holding 30% in permanent reserve is a real financial cost in exchange for protection that is rarely needed. For a household in regional QLD that loses power several times a year for hours at a time, that reserve is genuinely earning its keep.
The setting is not one-size-fits-all. The installer’s default was.
How to work out what yours should be
Two questions determine where your reserve level should sit.
1. How often does your grid actually fail?
Your electricity distributor publishes historical outage frequency data by area. Ausgrid, Endeavour Energy, AusNet, and CitiPower all have this information. Before deciding how much reserve to maintain, check how often the scenario it protects against actually occurs in your postcode.
A household in inner Melbourne or Sydney that experiences one brief outage per year doesn’t need the same reserve as a household on the fringe of the South Australian grid that loses power regularly in storm season. The backup capacity should reflect the actual risk.
2. How long do outages typically last?
25-30% of a 10 kWh battery is 2.5-3 kWh. That’s enough to run a fridge and basic lighting for roughly 3-4 hours. If your area’s typical outage is resolved within an hour, holding 25-30% in reserve is more protection than the situation requires. If multi-hour outages are common, it may be exactly right.
For most urban households on a stable grid, a reserve of 10-15% captures significantly more financial return while maintaining enough backup for a short outage. The battery’s daily usable capacity increases, the payback period shortens, and the protection level remains meaningful for the most common outage scenario.
Before you lower it, check two things
- Your battery’s warranty documentation: Some manufacturers specify a maximum depth of discharge that, if exceeded regularly, affects warranty coverage. Some build a hard hardware floor regardless of what the user sets in the app. Others allow full discharge but note that consistently cycling to very low states increases cell degradation. Check your specific model’s documentation before moving the reserve below 10%.
- Your VPP platform’s settings: If you participate in a virtual power plant, the VPP software manages its own discharge floor, which may interact with or override the battery’s built-in setting. Some VPP platforms will not export below a set threshold unless specifically instructed to do so. Reducing your battery’s reserve may have no practical effect if the VPP is setting its own limit. In some cases, you need to update the settings in both the battery app and the VPP platform separately to see any change.
When to change it temporarily
The minimum reserve level is worth revisiting beyond the initial setup in two specific situations.
The first one is when there’s a severe weather forecast. If a storm or extended cold snap is likely to stress the grid and increase the chance of an outage, temporarily raising the reserve to 50-80% before the weather arrives gives the battery meaningful capacity available if the grid goes down. Restore it to the normal setting once conditions pass.
The second one is when grid prices spike unusually. During a wholesale price surge, reducing the reserve temporarily lets the battery discharge further than usual to avoid buying expensive grid power at peak rates.
Both are one-time adjustments. The daily default should reflect your household’s ongoing situation.
How to find and change the setting
The setting name and location varies between battery systems, but the process follows the same general path:
- Open your battery’s monitoring app on your phone or tablet.
- Go to settings or configuration. Look for sections labelled “battery settings,” backup settings,” “energy mode,” or similar.
- Look for a reserve or backup percentage. It may be called “minimum reserve,” “backup reserve,” “reserved SOC,” or “discharge cut-off.”
- Adjust the percentage and save. Most apps confirm the change immediately.
If you can’t locate it after a few minutes, the setting is sometimes buried several menus deep or requires switching the system out of its default mode before it becomes editable. Your installer can access and adjust it remotely for most modern battery systems.
A good question to ask at your next system review: what is the minimum reserve currently set to, and does that still make sense for our situation?
Australia has installed more home batteries per capita than almost any country on earth. Most of them are running on the settings chosen on installation day, by an installer who didn’t know what your local outage history looks like, what tariff you would end up on, or whether you would join a VPP.
Checking that setting takes 5 minutes. For some, adjusting it will recover hundreds of dollars per year in electricity costs that the battery was always capable of saving.
