The consumption that no one pays attention to

A device that is merely switched on consumes power

Modern on-board electrical systems are efficient: inverters, charging boosters, and MPPT controllers are networked, can be monitored via app, and switch autonomously. However, if you look more closely, you will find that these devices draw power even when they are doing absolutely nothing. No consumer is running, no sunlight is falling on the panels, and yet the battery's state of charge drops. The reason for this is "base load" — and it is simply forgotten in most on-board power supply planning. It is not the same for every device: as a glance at current manufacturer data sheets shows, there are entire orders of magnitude between device categories.

Inverters and combi devices: the largest single item

An inverter that remains switched on permanently is, in most systems, by far the largest base load consumer. Manufacturer data sheets specify a "zero-load power" — i.e., consumption without any connected load — of around 6 to 10 W for pure inverters or combi devices in the medium power range (500 to 2,000 VA). At 12 V, that is 0.5 to 0.8 A just to keep the device ready. In the case of 4-in-1 devices, which also combine MPPT charge controllers and charging boosters in one housing, the consumption of the other components is added on top.

Almost all modern devices offer a search or eco-mode (often called "Search Mode," "AES," or similar) for this purpose, which cyclically switches the inverter on and off briefly as long as no significant consumer is active. According to the data sheet, this reduces the no-load consumption of the same device class to about 2 to 3 W — a reduction of around 70 percent, without losing a single function. The catch: this mode must be actively set; in many systems, it is not running because it was simply not configured during installation.

Practical valueIf you do not know whether the search/eco-mode is active, a power meter between the battery and the inverter for 24 hours will show it reliably. The difference between "Search Mode on" and "Search Mode off" is immediately visible on most devices.

Solar charge controllers, charging boosters, and battery monitors: small, but never zero

According to current data sheets, the internal consumption of MPPT solar charge controllers is typically 20 to 30 mA — regardless of whether the sun is shining or not, because the controller remains active in order to be able to charge immediately when light hits the panels. At 12 V, this is just 0.25 to 0.36 W.

With charging converters and charging boosters (B2B chargers) that connect starter and service batteries, the difference between off and on is particularly clear: when switched off, data sheets often state a quiescent current of less than 1 mA — practically immeasurable. However, as soon as the device is active and charging or waiting for charging conditions, the internal consumption rises to about 80 to 220 mA, depending on the model and input voltage. Camper-specific charging boosters that are permanently connected to the on-board power supply and monitor the ignition detection often state values of 3 to 7 mA for pure standby. The practical point: a booster that hangs in "waiting" mode on the grid for days because the vehicle is not moving draws the higher figure continuously — not the standby figure.

Battery monitors with shunts as well as pure display units are usually below 1 mA in the data sheets when the backlighting is switched off. Compared to inverters and active charging converters, they are the smallest component in the system.

Values from current manufacturer data sheets of various providers, rounded and dependent on device class — individual models may differ. The data sheet of the specific device installed is always the authoritative source.

The ranking is clear: the inverter or combi device component almost always dominates the base load, far ahead of everything else. Those who want to save should therefore first check whether the inverter's search/eco-mode is active — that is the lever with the greatest individual effect. Charge controllers and boosters contribute significantly less, but added up across several devices and several days, they reach a level that also becomes relevant during longer periods of inactivity.

What this means for the battery in total

FormulaDaily consumption (Wh) = current (A) × voltage (V) × 24 h

A realistic example system without activated eco-mode — inverter in normal operation (approx. 8 W), a charging booster in waiting mode (approx. 150 mA · 1.8 W), an MPPT charge controller (approx. 0.3 W), and a battery monitor (negligible) — totals about 10 W constant load. Over 24 hours, that is about 240 Wh per day — and that is before a cool box, lighting, or water pump has drawn a single watt. With the search/eco-mode activated on the inverter, this value is halved to around 120 Wh per day.

Even a large battery is not safe from this

This is precisely the trap many people fall into: one invests in a generously dimensioned battery bank, thinks one is on the safe side — and overlooks the fact that high base load consumes this reserve without any intervention. If a few cloudy days are coming up, the vehicle is parked in the shade, or it simply remains unused for a longer period, the technology continues to draw its base consumption while hardly anything or nothing is being recharged.

A 100 Ah battery at 12 V has around 1,200 Wh of usable energy (at 100% depth of discharge). With the roughly 240 Wh of base load per day from the example above, it is mathematically empty in about five days — without anyone having switched on a single consumer. Even a significantly larger bank only buys more time, not immunity: the base consumption simply continues regardless of the battery size.

What this means for planning and everyday life

For every design, this means first and foremost: the base load of the installed devices belongs in the energy balance right from the start — not just the consumption of what is actively used. Anyone dimensioning a solar system or battery capacity should include this base amount in the plan; otherwise, a gap will emerge in the end that cannot be explained. The most effective individual step is almost always to activate the search/eco-mode of the inverter if this was not done during installation.

For longer periods of inactivity — winter break, holidays at home, the vehicle simply standing around for a few weeks — a second look at the main switch is worthwhile. Anyone who disconnects the system completely from the grid instead of leaving it in standby stops this invisible consumption and will find the battery in a much better condition upon their return.

It is even more convenient with a remotely controllable main switch: devices that are not currently needed can be specifically disconnected from power without you having to be there or crawl under the seat bench. Especially with combi-inverters, which are often not actively used for days in everyday life but draw their base load continuously, this makes a noticeable difference for the battery — and can be controlled conveniently from a distance instead of relying on forgetting and hoping.

Conclusion

Modern on-board comfort has its price — even when nothing is running. The inverter contributes by far the most, followed by active charging boosters; solar charge controllers and battery monitors hardly matter. Anyone who activates the search/eco-mode, includes the base load in the solar and battery planning, and consistently uses the main switch during longer periods of inactivity will get noticeably more range out of every battery — without a single additional watt of solar power.