How much power does an inverter use when idle?

Most 1,000–2,000W pure sine wave inverters draw 10–30W at idle (no load connected). Over 8 hours, that's 80–240Wh — roughly 7–20Ah from a 12V battery. On a 100Ah LiFePO4 bank, this represents 7–20% of usable capacity consumed just by the idle inverter overnight.

Should I turn my inverter off when I'm not using it?

Yes, if your inverter doesn't have a search mode or low-power idle mode. Leaving a 20W idle inverter running 24 hours wastes 480Wh per day — about 10% of a 200Ah LiFePO4 bank. Switch it off before sleeping. Some inverters (Victron, Renogy with ECO mode) have a search/ECO mode that drops idle draw to 2–5W by pulsing to check for loads.

Inverter Standby Draw: Calculate the Battery Cost

An inverter can consume battery energy with no appliance running; multiply its actual idle watts by the hours it stays switched on.

An inverter running with nothing connected isn't free — it's converting DC to AC and maintaining voltage regulation, which uses power even with zero load. Understanding this helps you manage your battery more precisely.

Typical idle draws

Inverter size	Typical idle draw	8 hours overnight
400–600W budget inverter	5–15W	40–120Wh
1,000W pure sine	10–20W	80–160Wh
2,000W pure sine	15–30W	120–240Wh
3,000W pure sine	25–50W	200–400Wh
Victron MultiPlus 12/1600 (ECO off)	~10W	~80Wh
Victron MultiPlus 12/1600 (ECO on)	~2W	~16Wh

These are typical ranges — check your inverter's spec sheet for the exact "no-load power consumption" figure.

How much does this matter?

On a 200Ah LiFePO4 bank (160Ah usable at 80% DoD = 1,920Wh):

15W idle for 24 hours = 360Wh = 19% of usable capacity per day, just from the inverter sitting idle
15W idle for 8 hours (sleeping) = 120Wh = 6% of usable capacity

For a van that boondocks heavily, this is a meaningful drain. For a van that parks at campgrounds with shore power most nights, it matters less.

ECO mode / search mode

Many inverters include an ECO or search mode that drastically reduces idle draw by pulsing the AC output at low frequency (typically every 1–3 seconds) to check whether a load has connected. If no load responds, the inverter stays in low-power state.

Renogy inverters with ECO mode: idle drops to ~3–5W
Victron MultiPlus with ECO mode: idle drops to ~2W
Budget inverters without ECO mode: stay at full idle draw regardless

ECO mode works fine for most loads but can cause issues with some electronics that don't respond quickly to the pulsed output. CPAP machines, in particular, sometimes don't start correctly from ECO mode — test yours.

Practical recommendation

Default: Switch the inverter off at the main switch or via a 12V relay when you don't need it — when sleeping (no CPAP via inverter), driving, or if the van is parked and not being used. Install the inverter's remote switch in an accessible location so switching it on/off is convenient.

If you need it always on (CPAP at night, etc.): Enable ECO mode if available. A 2–5W idle draw is acceptable. If ECO mode causes CPAP startup issues, disable it and accept the higher idle draw as the cost of CPAP use.

Size the inverter for your loads: Larger inverters have higher idle draws for the same loads. A 3,000W inverter running a 500W laptop is wasting more idle power than a 1,000W inverter doing the same thing.

Worked planning check

An illustrative 12W idle load over 20 hours consumes 240Wh. At nominal 12.8V that is 18.75Ah before other loads. Compare this with the daily energy of the appliances you need overnight before leaving the inverter on continuously.

The figures or dimensions in this example are explicit planning assumptions, not a product test or an installation specification. Replace them with your equipment data and actual measurements.

Planning questions

How do I calculate inverter battery current?

Divide AC watts by assumed inverter efficiency and loaded battery voltage. Add other DC loads, and check starting surge separately. Use the result as a design input rather than a fuse recommendation.

Does an inverter use power with nothing plugged in?

Usually it has an idle consumption; check the exact model and operating mode. Multiply idle watts by hours switched on to include it in the daily energy budget.

Can any lithium battery run a large inverter?

No. Check BMS continuous and short-duration current, battery voltage, cable, protection and terminals. Energy capacity alone does not establish output capability.

Use the free electrical planner to organise your daily loads and charging assumptions.