Screen Time Maths
Maths hiding in screen time: battery percentages
Read battery as a percentage and estimate remaining time.
Quick answer
Battery percentages on screens show how much power is left, and you can use this to estimate how long your device will last before needing to be plugged in again.Learning outcome
By the end of this page, you will be able to read battery percentages and use them to make good guesses about how much more time you have left before your screen needs charging. Success signs:- You can say what percentage of battery is left on a screen
- You can estimate how long your device might last based on the battery level
- You can explain why battery percentages help you plan screen time
- You can compare different battery levels and tell which has more power left
Why this matters
Every day, you use devices with batteries – phones, tablets, laptops, game consoles, and even your smartwatch. Battery percentages help you understand how much power is left, so you know when to charge your device. This is useful for planning your screen time, especially when you're playing games, watching videos, or doing schoolwork. Knowing how battery life works helps you avoid your device running out of power at a bad moment – like during a video call or a fun game.How it works
Battery percentages show how much of the battery’s total capacity is still left. If a battery shows 100%, it is fully charged. If it shows 25%, it has only one-quarter of its full charge left. You can think of it like a water bottle – if it’s 50% full, it has half the water it can hold. The lower the percentage, the less time your screen will last. The percentage is calculated by comparing the current charge to the maximum charge the battery can hold. So if your phone has 40% battery and you know it lasts 2 hours at 100%, then at 40% it might last about 0.8 hours (or 48 minutes).Examples you can see
Let’s imagine you have a tablet with a battery that can last 4 hours when fully charged. Here are some examples of how the battery percentage affects how long it lasts:| Battery Level | Estimated Time Left |
|---|---|
| 100% | 4 hours |
| 50% | 2 hours |
| 25% | 1 hour |
| 10% | 24 minutes |
| 5% | 12 minutes |
Try it as a mini adventure
Adventure: Battery Detective You are a detective on a mission to find out how long your family’s devices will last. Here’s your task: 1st time: Look at your phone’s battery. It shows 75%. Estimate how long it might last if it normally lasts 3 hours when full. 2nd time: Check your tablet’s battery. It shows 40%. You know it normally lasts 2 hours when full. How much time is left? 3rd time: Your sister’s laptop shows 20%. It normally lasts 5 hours when full. How long will it last now? 4th time: What if your dad’s phone shows 90% and it normally lasts 4 hours? How long will it last? Solution: 1st time: 75% of 3 hours = 2.25 hours (or 2 hours and 15 minutes) 2nd time: 40% of 2 hours = 0.8 hours (or 48 minutes) 3rd time: 20% of 5 hours = 1 hour 4th time: 90% of 4 hours = 3.6 hours (or 3 hours and 36 minutes)Common mistakes
- Mistake: Thinking that 50% means the device will last half the time it normally lasts.
Why it happens: Children sometimes confuse percentages with halves or quarters without thinking about how to calculate the actual time.
Fix: Use simple multiplication. If a device lasts 2 hours at 100%, then at 50% it lasts 2 × 0.5 = 1 hour. - Mistake: Assuming all devices last the same amount of time at the same battery percentage.
Why it happens: Devices vary in size, usage, and power consumption.
Fix: Remember that battery life depends on the device and what you're doing with it. A tablet might last longer than a phone even if they both show 60%. - Mistake: Ignoring the percentage and just guessing.
Why it happens: Kids often rely on gut feelings or memory rather than using math to make estimates.
Fix: Use the percentage and think of it like a fraction or a part of a whole. If it’s 30%, think of it as 30 out of 100.
Parent and carer guide
As a parent or carer, you can help your child understand battery percentages by:- Using real devices to show how battery levels change as you use them
- Encouraging your child to estimate how long their screen will last based on the percentage
- Playing games like “Guess the Time” where you ask your child to estimate how long a device will last at different battery levels
- Using the battery percentages to teach fractions and decimals in a practical way
- Helping your child understand that lower percentages mean less time left
Practice questions
- If a tablet normally lasts 6 hours and shows 30% battery, how long will it last?
- A laptop shows 70% battery and normally lasts 4 hours. How long will it last?
- If a phone shows 10% battery and normally lasts 2 hours, how long will it last?
- What is 100% of 5 hours?
- If a game console shows 50% battery and normally lasts 8 hours, how long will it last?
- 30% of 6 hours = 1.8 hours (or 1 hour and 48 minutes)
- 70% of 4 hours = 2.8 hours (or 2 hours and 48 minutes)
- 10% of 2 hours = 0.2 hours (or 12 minutes)
- 100% of 5 hours = 5 hours
- 50% of 8 hours = 4 hours
FAQ
What does battery percentage mean?
Battery percentage shows how much of the battery’s total charge is left. If it says 50%, it means half of the battery’s full capacity is still usable.
How can I use battery percentages to plan screen time?
You can use battery percentages to guess how long your device will last. For example, if your tablet shows 40% and normally lasts 3 hours, you can estimate it will last about 1.2 hours (or 1 hour and 12 minutes).
Why do some devices show different battery levels at the same time?
Different devices use different amounts of power. A tablet may last longer than a phone even if both show 60% battery because of their size and how they are used.
Can I calculate battery time without a calculator?
Yes! You can estimate by thinking of percentages as parts of a whole. For example, 25% is a quarter, so if your device lasts 4 hours, at 25% it will last 1 hour.
How can I make learning battery percentages more fun?
You can play a game where you guess how long a device will last, or use real devices to test your estimates. You can also make charts showing battery levels and time left to see patterns.