TAU Power Bank: How Much Charge for a Day Out
By Rolling Square | The lifehackers company | Published: 2026-10-21
Category: How-to Guides
Wondering if a tiny keychain power bank can keep your phone alive all day? Here's how to estimate your needs and use the TAU effectively.
Quick answer
For a typical day out, the TAU power bank provides enough charge to top up a modern smartphone by about 30-50% — perfect for emergencies, not a full recharge.
Why size matters more than capacity for daily carry
Larger power banks often weigh over half a pound and won't fit in a jeans coin pocket, so they stay home when you're running errands. The TAU's keychain design means you always have it — and a charge you actually use beats a bigger battery you forgot. The tradeoff is limited capacity: you're trading raw milliamp-hours for portability.
Estimating your own daily phone drain
A typical smartphone uses about 15-20% battery per hour of active screen-on use (maps, social media, camera). If your day out involves 4 hours of active use plus standby, you might burn 70-80% of your phone's battery. The TAU can bridge the gap between your last top-up and getting home, but it's not built for heavy streaming or gaming marathons.
How to estimate and use TAU for a day out
- Check your phone's current battery before you leave: Note the percentage and estimate your typical daily usage (e.g., 4 hours of screen time). If your phone needs more than a 40% top-up to get through the day, plan a mid-day charging stop. Common mistake: assuming the TAU can fully recharge a phone from empty — it's a booster, not a full backup.
- Charge the TAU fully before heading out: Plug the TAU into a USB-C charger until its indicator light shows a full charge (about 1-2 hours). An empty TAU won't help when your phone is at 15%. Make charging the TAU part of your nightly routine, like charging your phone.
- Top up your phone before it hits 20%: Attach the TAU to your phone using the built-in cable when you see the low-battery warning. Let it charge for 30-45 minutes while you keep using the phone — the TAU's small size makes it easy to hold both together. Avoid waiting until the phone shuts off; the TAU may struggle to start charging a deeply depleted battery.
- Use low-power mode to extend the boost: On both iPhone and Android, enabling low-power mode reduces background activity and screen brightness. This can stretch the TAU's charge by 20-30%, giving you more usable time. Forgetting to enable low-power mode is the most common way users waste the TAU's small capacity.
Product facts
- TAU® - Always-charged power bank: TAU is the smallest power bank in the world, fitting on a key chain with a USB-C and patented Lightning + Micro USB cable. You can carry it everywhere without adding bulk, and it works with virtually any phone or small device right out of the box.
TAU® - Always-charged power bank
