Android 1.36.3 and later and iOS 1.38.0 and later hold up to 10 energy, enough for ten level starts without spending coins. On a fresh profile, the first twelve starts are free. After that, Start for a new attempt or restart costs one energy. Returning Home and continuing the same attempt spends none; Undo uses its tool charge, not energy. One energy returns every 20 minutes.
When upgrading an older energy save, five energy is added once, up to the new limit of ten. Your completed levels, coin balance and already-paid attempt are kept. Reopening the game does not grant another refill.
With an empty bar, you can wait for regeneration or choose the coin-to-energy exchange: one coin buys two energy. Preparation shows any cost before a new attempt.
Legacy mobile versions: The older three-mode Android app and iOS 1.30.0 hold up to five energy. They use the same twenty-minute regeneration interval; their older screens and start buttons may differ from the campaign.