FactRatedSmartphone Energy-Efficiency Classes Explained
A smartphone's A–G energy-efficiency class is not simply a ranking of battery runtime. It is based on an Energy Efficiency Index (EEI) that relates standardized battery endurance to the energy available from the battery.
That distinction matters. A phone can run for a long time because it carries a very large battery, while another can use a smaller battery more efficiently. The first may lead a runtime ranking; the second can still have the stronger energy-efficiency result.
For covered smartphones, A is the most efficient class and G the least efficient under the defined class thresholds.
| Energy efficiency class | Results |
|---|---|
| A | 400 |
| B | 384 |
| C | 137 |
| D | 65 |
| E | 35 |
| F | 19 |
| G | 17 |
Data source: EPREL · Last updated: Sep 7, 2026
What does the energy-efficiency index measure?
The applicable framework calculates the smartphone Energy Efficiency Index using:
- standardized battery endurance;
- nominal battery voltage;
- rated battery capacity.
In practical terms, the index relates the device's standardized runtime to the battery energy represented by its nominal voltage and rated capacity. The formal equation and unit conversions are defined in the regulation.
For consumers, the important interpretation is:
A higher efficiency index means the phone obtains more standardized runtime from the battery energy used in the calculation.
Smartphone A–G thresholds
For smartphones, the official energy-efficiency classes are based on the EEI bands below:
| Class | Smartphone EEI |
|---|---|
| A | greater than 2.70 |
| B | greater than 2.30 up to 2.70 |
| C | greater than 1.95 up to 2.30 |
| D | greater than 1.66 up to 1.95 |
| E | greater than 1.41 up to 1.66 |
| F | greater than 1.20 up to 1.41 |
| G | 1.20 or lower |
FactRated's initial normalized API contract reliably includes the registered energy class. If the underlying numeric EEI is not available as a canonical normalized source field, FactRated must not invent an intra-class numeric efficiency ranking.
Why class A does not always mean longest battery life
Consider two hypothetical phones:
- Phone A has an enormous battery and lasts 70 hours in the standardized test.
- Phone B has a smaller battery and lasts 60 hours but uses much less stored energy to achieve that runtime.
Phone A can win the absolute endurance ranking while Phone B can be more energy efficient.
This is why FactRated has separate pages for:
- longest standardized battery endurance;
- energy-efficiency class;
- battery-cycle durability.
One measurement cannot stand in for all three.
Why mAh still is not an efficiency score
Rated battery capacity tells you the amount of charge the battery is designed to store, typically expressed in mAh.
Efficiency depends on what the phone does with that energy.
A large battery can compensate for high consumption. A smaller battery can produce strong runtime if the phone is efficient. Looking at capacity without runtime gives you only one side of the relationship.
This is also why a list of phones sorted by mAh is not the same as a list sorted by energy efficiency.
Why smartphone and tablet classes should not be mixed
The energy-efficiency class thresholds for slate tablets are different from the smartphone thresholds.
For example, class A begins at a substantially different EEI level for tablets because the product category and test framework differ.
FactRated can display the same familiar A–G letters on smartphone and tablet pages, but it should not build a single combined "most efficient phones and tablets" ranking from those letters.
Rank within the correct device type.
Can software updates affect energy efficiency?
Yes, potentially.
The regulation requires the Energy Efficiency Index to be calculated using the operating-system version installed on the model at the relevant market point. If the operating system is updated while the model is still being placed on the market and that update changes the relevant parameters, the efficiency result and other label/product-information values can need reassessment.
For users, the important lesson is that registered product data is not necessarily a permanently frozen specification.
FactRated periodically synchronizes source data and displays freshness information rather than assuming the first imported class can never change.
Is a better energy class always the better purchase?
No.
Energy efficiency is one objective characteristic. A buyer may also care about:
- battery endurance per charge;
- battery-cycle durability;
- repairability;
- software support;
- IP protection;
- drop resistance;
- replaceable battery.
A class A phone with weak results on a user's top priorities is not automatically the right choice.
FactRated does not convert the energy class into an overall recommendation.
How to use the energy class in FactRated
If you care about efficient use of battery energy
Start with the A–G class.
If you care about time away from a charger
Use standardized battery endurance.
If you care about battery aging
Use battery endurance in cycles.
If you care about long ownership
Combine efficiency with cycle durability, repairability and software support.
Why FactRated may group rather than rank within a class
A class is a band. If the API provides class C for two products but does not provide a canonical numeric EEI value, FactRated knows they belong in the same class but does not know which has the higher EEI within that class.
It would be misleading to invent precision by using another metric as though it were the missing EEI.
Therefore the energy-efficiency landing can:
- group products A through G;
- sort classes correctly;
- show battery endurance/capacity as additional columns;
- clearly label any secondary sort as a different metric.
That is more transparent than manufacturing a "C1 vs C2" efficiency order without the source value.
Frequently asked questions
Is energy class A the best smartphone battery life?
Not necessarily. Class A is the most efficient energy class; the phone with the longest standardized runtime can be in another class if it achieves that runtime with more battery energy.
Does a bigger battery improve the energy class?
Not automatically. Battery capacity is part of the efficiency relationship, so simply increasing battery size does not guarantee a better efficiency index.
Are smartphone and tablet energy classes directly comparable?
The A–G labels look the same, but the EEI thresholds differ between smartphones and slate tablets. FactRated keeps the category rankings separate.
Can the energy class change after a software update?
The applicable framework allows relevant parameters to be reassessed when an operating-system update changes the product's measured/calculated performance while the model remains on the market.
Why doesn't FactRated create an efficiency score inside each class?
FactRated will only do that if a canonical numeric source value supports it. It does not invent additional precision from unrelated metrics.
Related FactRated pages
- Most energy-efficient smartphones
- Smartphones with the longest standardized battery endurance
- How to compare smartphone battery life fairly
- Find phones by energy class
Sources and methodology
The energy-efficiency class thresholds and EEI calculation framework come from Commission Delegated Regulation (EU) 2023/1669. FactRated uses the registered class from normalized source data and does not invent a numeric EEI when the canonical API field is unavailable.
Data source: EPREL · Last updated: Sep 7, 2026