Log every charge. Understand every kilometre.
Track EV charging sessions, efficiency, cost, and CO₂, one joule at a time. Built and maintained by the Sustainable Power Systems Lab (SPS-Lab) at Cyprus University of Technology.
🌐 Live site: sps-l.github.io/joulie
Joulie is a clean, no-nonsense Android app for electric vehicle drivers who want to know exactly how their car uses energy. Log each charge and Joulie tracks the numbers that actually matter.
What you log per charge:
- Odometer reading, kWh added, AC or DC session
- Location (quick-chips or free text), and optional cost
- State-of-charge percentages, if your charger only shows %, Joulie does the kWh math for you
What Joulie shows you:
- Efficiency in km/kWh, kWh/100 km, or mi/kWh across any time period
- Cost per km or per 100 km, with mixed-currency warnings when relevant
- AC vs DC breakdown charts, monthly kWh and cost trends, and battery degradation over time
- CO₂ emissions versus a petrol-car baseline, fed by an opt-in Electricity Maps live grid-intensity feed (zone-pick your region; on-device 1-hour cache so you don't burn API quota)
- A dashboard pill showing the current grid intensity colour-coded across five bands, so you know at a glance whether now is a good time to charge. Every charge event is logged with the grid intensity at save time.
Other features:
- Multi-car support with a top-bar switcher
- Home-screen widget showing your last charge at a glance
- kWh-from-SoC calculator for chargers that show only state-of-charge percentages
- Optional Google Drive backup (opt-in, stored in your private App Data folder only)
- CSV export via the standard Android share sheet
- Material 3 theming with light, dark, and system modes
- Themed icons on Android 13+; the bolt-J adopts your wallpaper accent
- Available in English, Greek, Turkish, and Russian
Privacy by design. No analytics, no telemetry, no crash reporting. Your charge data stays on your device unless you explicitly enable Drive backup.
Drive smart. Charge logged. Every joule counted.
Signed release APKs are attached to every GitHub Release: see the Releases page.
adb install joulie-vX.Y.Z.apkYou can also open the APK on the device after enabling Install from unknown sources for your file manager or browser.
- The app does not collect analytics, telemetry, or crash reports.
- All charge data is stored locally in the app's private Room database.
- Google Drive backup is opt-in. When enabled, a JSON snapshot is written to the app's private App Data folder on your Drive, hidden from the Drive UI and accessible only to this app's signing certificate. The scope is
https://www.googleapis.com/auth/drive.appdata, the app cannot read or modify any other files on your Drive. - The Electricity Maps grid-intensity feed is also opt-in. When enabled, the only payload sent off-device is
(zone_code, api_key), for example"CY"plus the personal API token you typed in. No charge data, no location, no personally-identifiable information. Calls are throttled to one request per zone per hour and the result is cached locally. - CSV export writes to the app's external-files directory and is shared only via the Android share sheet at your request.
Full policy: PRIVACY.md, or live at sps-l.github.io/joulie/privacy.
Released under the GNU General Public License v3.0 or later (GPL-3.0-or-later). © 2024–2026 Sustainable Power Systems Lab (SPS-Lab), Cyprus University of Technology.
This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. It is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the LICENSE file for the full text.
Building from source, running tests, or contributing? See CONTRIBUTING.md.