In short
- Count only the usable part of the bank: the inverter stops long before the cells are empty.
- The inverter itself draws power around the clock, often 30 to 60 W.
- Evening peaks drain the bank faster than the night average suggests.
Runtime sounds like simple division. Three corrections make the difference between the number on paper and what you actually get.
1Usable, not nominal
Your inverter stops discharging at a cut-off, often somewhere between 10 and 20 % depending on how it is set. A bank of three 5 kWh packs stopped at 15 % gives about 12.75 kWh, not 15. If the batteries are a few years old, multiply by the state of health as well: a pack at 95 % holds 95 % of its original capacity.
2The inverter never sleeps
A hybrid inverter draws its own power around the clock: often 30 to 60 W, sometimes more with the fans running. Over a twelve-hour night that is up to 0.7 kWh, gone before the fridge has used a watt.
3The evening is not the night
Between six and ten in the evening a house cooks, washes and lights up. A 600 W night average can hide a 2 kW peak at dinner time. Those first four hours often use as much as the eight that follow. That is why a bank that “should last until morning” runs out at four.
Doing the sum for your house
EG4 Monitor shows the bank’s charge and power minute by minute. Look at a normal evening: note the charge at sunset and at sunrise, and the hours in between. That ratio is your real runtime, with your own habits in it. Then try the runtime calculator on this site with your figures, to see what one more pack or a later cut-off would change.
Making it last longer
Moving the dishwasher or the car to midday, when the panels cover them, does more for your nights than any setting. A notification at nine in the evening when the bank is below a level you choose gives you time to act before the cut-off.
Common questions
Does EG4 Monitor show the time left?
Yes: the dashboard estimates when the bank will be full or reach its cut-off at the current pace.
Should I set a lower cut-off to gain hours?
Follow EG4’s recommendations for your packs. Going deeper every night gains hours but costs cycles over the years.
Why do my packs show different charge levels?
Packs in parallel never share the load perfectly. Small differences are normal; our guide on EG4 batteries in parallel explains what to watch.
