An inverter sitting switched on with nothing plugged into it still eats your battery. On a 3000VA Victron Inverter Smart at 12V that is 12 watts, which is 288 watt-hours over a full day. Run our numbers on a 12V fridge and you get 20 to 24 amp-hours a day, which at 12V is 240 to 288 watt-hours. Your idle inverter costs about what your fridge costs. That is the part people leave out of the power budget.
The spec sheet name for it is zero load power, and Victron publishes the whole table. From the Inverter Smart technical specifications, verified today, listed by system voltage:
- 1600VA and 2000VA: 8W at 12V, 9W at 24V, 11W at 48V
- 3000VA: 12W at 12V, 13W at 24V, 15W at 48V
- 5000VA: 18W and 20W for the two voltages published
Multiply by 24 hours. The 1600VA costs 192Wh a day doing nothing. The 3000VA costs 288Wh. The 5000VA costs 432 to 480Wh. None of that has powered anything.
This is a separate cost from conversion loss
Two different things get confused here. Conversion loss is a percentage: the same page lists maximum efficiency of 92 percent at 12V for the 1600VA and 2000VA, and 93 percent at 12V for the 3000VA. So a 100W AC load pulls at least 109W from the battery, and that is the best case, not the typical one.
Zero load power is a constant. It runs whether you are drawing 1000W or nothing at all, and it runs all night while you sleep. People budget the percentage and forget the constant, then wonder why the battery is lower at sunrise than the arithmetic said.
ECO mode, and its catch
The same table lists ECO mode figures of 0.6W for the 1600VA and 2000VA at 12V, and 1.5W for the 3000VA. That takes the 3000VA from 288Wh a day to 36Wh.
The operation section of the manual, verified today, explains how: “The inverter will automatically switch off as soon as it detects that there is no load connected. It then switches on, briefly, every 3 seconds to detect a load.”
That is the catch. A small always-on load may sit below the wake threshold. The manual says it plainly: “If the inverter keeps switching on and off while there is a load connected, the load may be too small compared to the actual ECO mode settings.” If you leave a phone charger or a low-draw appliance on the AC side, ECO mode can chatter instead of settling. Raise the threshold setting or accept the standby draw for that circuit.
The honest limits on these numbers
These are Victron’s published figures for one product family. A budget inverter can idle higher, and plenty of them do not publish a zero load figure at all, which usually means the number is not flattering. Find your own unit’s datasheet and look for zero load, no load, or standby power. If nobody published it, measure it: switch every load off, read the battery monitor with the inverter on, then switch the inverter off and read it again.
If your inverter has ECO mode, turn it on and set the threshold above your smallest real load. If it does not, put it on a switch and leave it off unless you are using AC. Then rerun the whole budget with our RV solar calculator, and read our power budget guide for where the other constants hide.