Know exactly how long your battery or generator will last. Input your devices, set capacity — Tower Energy shows your precise runtime before the lights go out.
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Tower Energy is built on a watt-hour runtime engine that gives you a precise answer to a simple question: how long will my power last? Enter your battery or generator's total capacity in Wh — the app ships with real-world presets like Fosibot — then add every device you plan to run. The runtime counter updates instantly with each change, no server call, no delay.
The Time Simulation slider lets you scrub through projected usage hours at any point in the future. The orange hour counter tracks your position against the calculated maximum — 6h 40m at a 300 W load — while the remaining Wh readout on the left and max runtime on the right keep the math fully visible. Drag forward two hours and see exactly how much capacity you'll have left by morning.
Everything runs offline. Tower Energy stores your configured sources and device list in local device storage — no account required, no connectivity needed when the grid actually goes down. The app installs at just 6.1 MB and supports iOS 15.6 and above, making it practical to have ready on any iPhone before an outage ever starts. Fans of energy management tools may also enjoy Tower Energy's companion utilities from the same developer.
Name your power source — select from built-in presets like Fosibot or enter a custom name — and specify capacity in Wh. An efficiency slider (default 100%) lets you account for real-world battery losses, so your runtime estimate reflects actual usable power, not just nameplate capacity.
Add appliances by selecting from the built-in device library or entering custom wattage values. Set each device to Continuous or Intermittent mode — Continuous counts the device as always drawing power, while Intermittent applies a partial-use factor to reduce its contribution to the total load.
The Estimated Runtime display updates in real time as you add or remove devices and adjust capacity. At 2000 Wh with a 300 W TV running continuously, the output reads 6h 40m — change any variable and the number recalculates immediately, displayed in large neon-green numerals against the dark dashboard.
Drag the white-handle slider forward across the projected timeline to simulate energy state at any future point. The orange hour counter and remaining Wh readout update in sync, showing exactly how much capacity you'll have left at 2 hours, 4 hours, or any point up to your calculated maximum runtime.
Two large circular gauges — Total Capacity (kWh) and Consumption (W) — display live values with glowing cyan arc rings on a dark-field background. A dedicated consumption percentage gauge shows your current load as a portion of total capacity, with a red arc indicator marking the active draw percentage.
Load a complete device configuration instantly with one tap. The Home preset populates 5 devices including Refrigerator (150 W), LED Lights (60 W), and Router (15 W). Emergency loads 4 critical devices. Camping loads 5 field-use devices. Each profile fills the device list immediately, ready to adjust.
Svitlana Kravchenko built Tower Energy as a focused iOS utility — no corporate platform, no subscription, no account requirement. The app targets iPhone users on iOS 15.6 and later, installs at 6.1 MB, carries a 4+ age rating, and is available at no cost. Copyright 2026. The Travel category placement reflects the app's primary use case: calculating power duration for field scenarios, camping trips, grid-independent living, and blackout preparedness wherever you are.
Free on iPhone. iOS 15.6 or later. No account, no setup fees. At 6.1 MB it installs in under 30 seconds — be ready before the next outage.
Download for iOS — Free
Requires iPhone · iOS 15.6 or later · Free — no in-app purchases
Age rating: 4+ · iPhone optimized · 6.1 MB · Developer: Svitlana Kravchenko