When Your App Needs an Energy System

Duolingo switched from unlimited lessons to an energy system where users have limited hearts. Make too many mistakes and you need to wait for hearts to regenerate or complete practice exercises to restore them.

This change was controversial but effective. The limitation created more intentional learning—users paid closer attention to avoid losing hearts. It also created natural session endpoints rather than endless grinding.

Energy systems meter usage rather than reward it. This makes them fundamentally different from XP or achievements. Understanding when metering drives better engagement is key to using energy effectively.

Key Takeaways:

• Energy systems work by creating scarcity and natural session boundaries
• They're most effective when usage patterns benefit from intentional pacing
• Balance is critical—too restrictive frustrates users, too generous defeats the purpose
• Implementation takes 1-2 months building or 1 week with platforms like Trophy
• Energy can be earned through valuable actions, not just time-based regeneration

What Energy Systems Do

Energy creates a depletable resource that gates usage.

Usage metering: Energy limits how much users can engage in a session. Each action consumes energy. When energy depletes, users must wait for regeneration or complete alternate actions to restore it.

Natural stopping points: Rather than users deciding when to stop, energy depletion creates clear session endpoints. This prevents burnout from excessive use.

Increased engagement value: Scarcity increases perceived value. When usage is unlimited, individual sessions feel less significant. Limited energy makes each use feel more valuable.

Monetization opportunity: Many energy systems let users purchase additional energy or skip regeneration timers. This creates optional monetization without requiring paywalls.

Behavior pacing: Energy forces users to distribute engagement over time rather than consuming everything at once. This can improve learning retention, prevent fatigue, or extend content lifespan.

When Energy Makes Sense

Energy systems work for specific product goals and usage patterns.

Learning platforms: When users benefit from spaced practice rather than cramming, energy encourages optimal learning patterns. Short, regular study sessions work better than marathon study sessions for retention.

Content consumption with limited catalog: If your content library is finite and users could exhaust it quickly, energy extends engagement over time rather than having users binge everything immediately.

Freemium monetization: Energy provides conversion opportunities. Free users have limited energy. Subscribers get unlimited energy or faster regeneration. This creates clear paid tier value.

Preventing burnout: For intensive activities (difficult puzzles, challenging workouts), energy prevents users from overextending and burning out.

Habit formation: Energy that regenerates daily encourages users to return regularly. The renewable resource creates reason to check back.

Energy works when intentional usage pacing benefits users or extends engagement with limited content.

When Energy Backfires

Energy systems create frustration in several contexts.

Utility products: If your product solves immediate needs (task management, note-taking, communication), energy blocking usage creates frustration. Users need unrestricted access to functional tools.

Already scarce engagement: If users struggle to engage regularly, limiting their engagement when they do show up is counterproductive. Energy works when you have too much engagement to distribute, not when you're fighting for any engagement.

Content abundance: If you have unlimited content, energy doesn't serve a purpose. Users won't exhaust your catalog, so metering access just creates friction.

Professional contexts: B2B products where usage represents work output shouldn't use energy. Limiting how much work users can complete damages perceived value.

Goal-oriented products: When users are pursuing specific outcomes (weight loss, learning a skill), artificial limitations feel like obstacles to their goals rather than helpful pacing.

Balancing Regeneration Rates

The core challenge with energy systems is finding the right regeneration rate.

Too restrictive: If energy depletes in minutes and takes hours to regenerate, users can't build meaningful engagement. They'll abandon rather than wait.

Too generous: If energy rarely depletes or regenerates instantly, the mechanic doesn't affect behavior. You've added complexity without impact.

Usage patterns matter: Study how long typical sessions last naturally. Energy should support slightly longer sessions than average, giving users room for extra engagement when motivated.

Start generous: Launch with more generous energy limits. It's easier to tighten restrictions based on data than to loosen them after users complain about frustration.

Test with users: Different user segments might need different energy amounts. Power users need more energy to maintain engagement. Casual users need enough to complete meaningful sessions.

Trophy's points system supports energy mechanics with configurable regeneration rates, letting you test different balances without code changes.

Regeneration Strategies

How energy regenerates affects user behavior.

Time-based regeneration: Energy regenerates per hour or per day. This creates predictable rhythms—users know when they'll have full energy again.

Action-based regeneration: Users restore energy by completing specific actions (practicing skills, watching ads, helping others). This encourages valuable behaviors.

Hybrid approach: Combine time-based regeneration with action-based restoration. Energy regenerates slowly over time, but users can restore it faster through actions.

Daily reset: Grant full energy each day at a consistent time. This creates daily engagement patterns rather than continuous regeneration.

Session-based: Energy depletes during sessions but fully restores between sessions. This creates natural breaks without long wait times.

The right strategy depends on your desired usage patterns. Daily habits benefit from daily resets. Continuous engagement benefits from hourly regeneration.

Energy Consumption Design

What consumes energy and how much significantly impacts user experience.

Per-action consumption: Each user action (complete lesson, play level, take quiz) consumes fixed energy. Simple and predictable.

Performance-based consumption: Mistakes or poor performance cost energy. Good performance preserves energy. This encourages quality over quantity.

Variable consumption: Different actions consume different amounts. More valuable or intensive actions cost more energy.

Difficulty-based: Harder challenges cost more energy but provide greater rewards. This creates trade-offs between efficiency and challenge.

Streak protection: Maintaining streaks doesn't consume energy, encouraging consistent engagement without penalizing streak-maintainers.

Duolingo's heart system combines several approaches—mistakes cost hearts (performance-based), but streak-maintaining practice exercises don't cost hearts (streak protection).

Maximum Energy Capacity

How much energy users can hold at once affects engagement patterns.

Lower capacity, faster regeneration: Small energy pools (5-10 units) that regenerate quickly create frequent engagement opportunities. Users can fully engage multiple times daily.

Higher capacity, slower regeneration: Larger pools (50-100 units) that regenerate slowly support longer sessions but less frequent play.

Expandable capacity: Let users increase max energy through progression or purchases. This rewards long-term engagement while monetization.

Overflow prevention: Don't let regenerating energy exceed maximum capacity. This creates incentive to use energy before it caps, driving engagement.

The right capacity depends on session length. If ideal sessions consume 10 energy units, max capacity should support 15-20 units—enough for extended sessions without making the limitation irrelevant.

Display and Communication

How you communicate energy status affects user experience.

Prominent visibility: Show current energy and maximum capacity clearly. Users need to know their status at a glance.

Regeneration clarity: Tell users when they'll have more energy. "Full energy in 2 hours" provides clear expectations.

Consumption preview: Before actions that consume energy, show how much they'll cost. This prevents surprise depletion.

Low energy warnings: Alert users when energy is nearly depleted. This gives them chance to optimize remaining energy use.

Restoration paths: Clearly show how users can restore energy faster (complete practice, watch ad, purchase). Make alternatives obvious.

Clear communication prevents frustration. Users accept limitations when they understand the system and have agency within it.

Monetization Considerations

Energy systems often include purchase options.

Energy purchases: Let users buy energy directly. This provides immediate relief from limitations.

Regeneration speed-ups: Let users purchase faster regeneration rates. This ongoing benefit can drive subscription value.

Capacity increases: Sell permanent capacity increases. This one-time purchase appeals to users who want less restriction.

Subscription removal: Offer unlimited energy as subscription benefit. This creates clear premium tier differentiation.

Earning alternatives: Always provide non-payment ways to restore energy. Watching ads, completing tasks, or waiting should be viable options.

Balance monetization against user experience. Energy shouldn't feel like punishment for not paying—it should feel like beneficial pacing with optional acceleration.

Learning from Duolingo

Duolingo's energy system (hearts) teaches several lessons.

They launched with unlimited lessons, then added hearts system. This was controversial but data showed improved learning outcomes. Users made fewer careless mistakes when hearts were at stake.

Hearts regenerate over time but users can also restore them through practice exercises. This creates engagement even when hearts are depleted—practice becomes valuable rather than just a regeneration wait.

Subscribers get unlimited hearts, creating clear premium value. Free users aren't blocked entirely but face meaningful limitations.

The system encourages daily engagement because hearts fully regenerate daily. Users return to use their restored hearts rather than letting them sit unused.

Alternative Metering Approaches

Energy isn't the only way to meter usage.

Daily limits: Cap actions per day rather than using regenerating energy. Simpler but less flexible.

Cooldowns: Individual actions have cooldown timers rather than shared energy pool. This works for products with few distinct actions.

Turn-based: Users get fixed turns per period. Used in multiplayer contexts where timing matters.

Content gates: Lock content behind time gates rather than energy. Each piece of content becomes available on schedule.

Session caps: Limit session duration rather than action count. Simple but less granular than energy.

Energy's advantage is flexibility—you can meter different actions differently while providing multiple restoration paths.

Implementation Challenges

Building energy systems involves several technical considerations.

Real-time tracking: Current energy needs to be accurate and update immediately as actions consume it.

Regeneration calculation: You need server-side logic to calculate regenerated energy based on elapsed time, even when users aren't active.

Time zone handling: If regeneration happens at specific times (daily reset), handle time zones correctly so all users get fair treatment.

Consumption rules: Different actions consuming different energy amounts requires flexible configuration that lets you balance the system.

Purchase handling: If users can buy energy, you need purchase flow integration and immediate energy delivery.

Building energy infrastructure typically takes 1-2 months. Trophy handles all this infrastructure, reducing implementation to 1 day to 1 week—configure energy rules, integrate the SDK, build UI to display energy status.

Measuring Energy System Effectiveness

Track these metrics to understand if energy drives desired behaviors.

Depletion frequency: How often do users run out of energy? If most users never deplete, the limitation doesn't affect behavior.

Session length: Compare session lengths before and after energy implementation. Energy should create more consistent, appropriate-length sessions.

Return rate: Do users return after energy depletes? High return rates indicate energy creates effective engagement pull.

Restoration paths: How do users restore energy—waiting, completing actions, or purchasing? This shows which restoration mechanics drive engagement or revenue.

Frustration signals: Watch for frustration indicators—users abandoning after depletion, negative feedback, decreased retention. These signal energy limits might be too restrictive.

Trophy provides analytics on energy consumption, restoration patterns, and how energy impacts user behavior.

Getting Started with Energy

If energy aligns with your product goals, here's how to implement effectively.

Define core actions: Identify what should consume energy. Start with 1-3 action types rather than complex systems.

Choose consumption rates: Assign energy costs to each action. Start simple with equal costs, then adjust based on action value.

Set capacity and regeneration: Pick maximum energy and regeneration rate. Start generous—you can tighten later based on data.

Design restoration paths: How can users restore energy? At minimum: time-based regeneration. Optionally: earned restoration through specific actions.

Build clear UI: Show energy prominently, communicate costs clearly, and make restoration paths obvious.

Launch to small group: Test with subset of users first. Measure depletion patterns, session lengths, and return rates before full rollout.

Trophy's pricing is based on monthly active users, letting you test energy mechanics at small scale before committing to broader rollout.

Frequently Asked Questions

How much energy should users start with each day?

Enough to support 1-2 meaningful sessions. If your typical session consumes 10 energy units, start users with 20-30 units daily. Monitor depletion data and adjust. Most users should deplete energy some days but not others.

Should energy deplete to zero or have a minimum reserve?

Depleting to zero is simpler and creates clearer stopping points. Minimum reserves (can't go below 1 energy) prevent complete blocking but reduce the mechanic's impact. Most successful implementations allow full depletion with clear restoration paths.

Can energy systems work without monetization?

Yes, but they're less common. Energy can drive engagement patterns (daily habits, session pacing) without monetization. Just ensure users have free restoration paths beyond waiting—completing valuable actions should restore energy.

How do we prevent frustration when users run out of energy?

Provide clear restoration paths, communicate when energy regenerates, and ensure users can still accomplish something while waiting (practice exercises, content viewing, community interaction). Never completely block valuable product usage.

Should different user segments have different energy amounts?

This creates complexity and potential fairness concerns if users compete. Better to offer consistent energy limits but let users expand capacity through progression or subscriptions. Treat all users at the same tier equally.

What if users stop engaging because energy limits frustrate them?

Watch retention data closely after implementing energy. If retention drops, your limits are too restrictive. Start generous and tighten gradually rather than starting restrictive. Users accept tightening more than they accept restrictive starting points.

Can energy systems work in B2B products?

Rarely. B2B users expect unlimited access to functional tools they're paying for. Energy feels like artificial restriction on productivity. The exception might be resource-intensive features (API calls, AI processing) where real costs justify limits.

How do we communicate energy limits to users initially?

Introduce energy gradually. Let users engage without limits initially to build habit, then introduce energy with clear explanation of benefits ("helps you learn more effectively through spaced practice"). Grandfather early users with generous energy if possible to reduce resistance.