Parasitic Draw Cost Calculator
Convert 24/7 standby current into daily Wh and monthly € cost at your kWh price. Great for finding and killing vampire loads in van electrical systems.
mA vs A — which should I enter?
Either is fine. If your spec says **mA**, select **mA** so the calculator converts automatically. Example: 150 mA = 0.15 A.
Why does 12 V make small currents look expensive?
Even a few hundred mA, running **24/7**, adds up. Power = **I × V**; multiply by 24 hours × 30 days and it becomes real money (and battery drain off-grid).
Do I include devices that sleep?
Use the **typical idle** value, not peak. If a device cycles (e.g., modem reconnects), take an average or measure with a DC meter/logger over a day.
How accurate is this?
Within the accuracy of your current reading and price. Voltage and idle current can drift with temperature; treat results as **±10–20%**.
What’s a “good” standby budget for a van?
Aim for **<5 W total** when parked if you rely on battery for days. Over **10–15 W** idle often means you should rework switches and device settings.