Why isn't my battery saving me money?

Question

Accepted Answer

Your battery may be saving little because it charges at the wrong price, runs out before expensive periods, stays full when solar arrives, or has too little costly household demand to replace. Some homes will not save much even with good control: low consumption, a narrow tariff price gap or valuable solar export can leave little financial benefit after losses and costs.

Find out whether the problem is energy or money

Start with a day you can explain. Read your supplier's import and export records alongside the battery's charge level and the inverter's history. Import is electricity bought from the grid; export is electricity sent back. The inverter manages conversion between the battery and your home's electrical supply. A kilowatt-hour, or kWh, measures energy, while a tariff is your supplier's pricing agreement.

Check whether the battery charged, when it discharged and whether the house still imported during expensive periods. Then attach the prices that applied at those times. A chart showing more solar self-consumption can look encouraging without proving lower costs. Conversely, deliberate grid charging can increase imported energy while reducing the bill if it replaces more expensive purchases later.

Check what you are comparing

A larger bill does not by itself mean storage has failed. Weather, heating demand, household routines and supplier prices can change at the same time. Compare the observed energy flows with what the same household demand and solar generation would have cost without that battery schedule. Keep the standing charge, a fixed supplier charge, separate where it is unchanged by battery use.

If you recently changed tariffs, distinguish savings from the tariff switch from savings caused by storage. If you already had a useful charging timer, the additional value of an optimiser is the improvement over that timer. Comparing everything with an expensive, unrealistic alternative can make the result look much better than the decision you actually face.

Look for a schedule that no longer fits

A fixed overnight charge can make sense on a predictable cheap window. It can also fill the battery just before a sunny day, leaving no room for surplus solar. An overly cautious reserve can leave purchased electricity unused while the house imports. A reserve is charge deliberately held back, often for resilience; lowering it changes that protection and should be a conscious choice.

Check the configured tariff, clock, charging windows and charge target. Look for another controller or an inverter schedule overriding the settings you intended. Inspect changes in household routine too: an evening meal, heating or vehicle charging may now use energy after the battery has emptied. Review normal operating settings, and involve the installer if readings or equipment behaviour appear wrong.

Check the physical limits before blaming the algorithm

Storage capacity and power are different constraints. Capacity determines how much energy the battery can hold; power determines how quickly it can charge or supply the home. A battery with energy remaining may still be unable to cover a short burst of household demand. A cheap interval may be too short to reach the desired charge level.

Temperature, configured limits and equipment protection can also restrict operation. Energy is lost during charging and discharging, so shifting electricity between similar prices may not save money. Do not remove protective limits to chase a better graph. Ask whether the observed behaviour follows the equipment's specification and the settings agreed with your installer.

Make sure solar and export are valued correctly

Using every unit of solar at home is not always the lowest-cost outcome. If exporting it earns more than the cost of buying electricity later, after accounting for storage losses, filling the battery from solar can sacrifice value. Equally, exporting stored energy now can be a poor choice if you then buy expensive electricity to cook or heat the home.

Use your actual export agreement, including whether battery exports qualify for payment. An import tariff's changing prices do not establish what export will earn. The useful comparison is the overall net electricity cost across the period, with both buying and selling included, rather than a single self-consumption percentage or an isolated export payment.

Recognise when there is little left to optimise

If your household uses most electricity directly during solar generation, there may be little expensive demand left for the battery to replace. If cheap and expensive import prices are similar, losses can consume the difference. If your existing controls already match your routine well, changing software may add little. In those situations, disappointment can reflect limited opportunity rather than a hidden configuration fault.

PredBat uses prices, demand and solar forecasts to update the battery plan automatically. Across 392 active instances on 29 August 2026, the observed median saving was £1.24/day, with a lower quartile of 49p and an upper quartile of 231p. Those quartiles describe the spread of that dated fleet observation. They are neither minimum nor maximum savings, nor a promise for your home. The service costs £9.99/month, which must be justified by your own additional benefit.

Decide what to change from the evidence

Keep a record of the schedule, prices, energy flows and net cost before and after a setting change. Include both sunny and dull conditions and different household routines. If a change only looks good when compared with a different season or tariff, you have not yet isolated its effect.

Correct a wrong tariff or conflicting schedule first. Then consider whether forecasting could improve the remaining decisions. If the equipment is functioning and the economic margin remains small, accepting modest savings may be the honest conclusion. Buying more capacity or another service without identifying the constraint can simply increase the amount you need to recover.

Why isn't my battery saving me money? | PredBat