How we test batteries
By Sarah Ingrams
Find out how we test batteries to find the best and longest-lasting ones for your devices. Only the best batteries become Best Buys.
Only the batteries that last the longest and power your devices without any problems can be rated as Best Buys.
We’ve tested a range of AA batteries and AAA batteries in the Which? test lab, using a strict range of criteria so you can be sure that the ones you buy really do last the distance in your devices.
We analyse more than 1.5m data points in our tough tests so our reviews can answer your most crucial questions about batteries:
- How long will the batteries last in my devices?
- Will they leak and damage my devices?
- Which batteries are best value for money?
- Should I buy them?
Want to know which batteries are best? Go straight to our disposable batteries reviews to find out which ones are good enough for Best Buy status. Or take a look at our rechargeable batteries reviews. To find out more about our testing, read on.
How long will the batteries last in my devices?
Your alarm clock, remote control and child’s battery-powered toy need different amounts of energy, which they use at different rates. We test disposable batteries in three different conditions that mimic the devices you’re most likely to use them in – so you know which will power your devices for longest.
Our high-drain tests measure how long disposable batteries last in the most power-hungry devices, such as remote-controlled toys. Medium-drain mimics items such as lighting or games console handsets. Low-drain tests show how batteries last in devices such as clocks and clock-radios - these use a small and steady amount of power over a long period.
1.5 millionThe number of data points we analyse in our disposable batteries tests to find the best
We time how long it takes each battery to run down to 1V (when most devices stop working) and their end voltage (when all devices stop working). The best AA disposable batteries last more than three hours longer than the worst in the most power-hungry devices. Find out which ones we’re talking about - see our Best Buy batteries.
Of course, our tests can’t simulate every single device that uses batteries. So we also calculate the amount of energy each battery contains, taking into account all our test results. This means you can use our test results to choose the batteries that pack the most power.
Will the batteries leak and damages my devices?
Leaking disposable batteries have caused 28% of Which? members a problem in the past two years (online survey of 1,292 Which? members, August 2015). Our survey revealed that batteries are most likely to leak when they're discharged - most of our members found that their batteries leaked after being left in a device, as opposed to unused in a drawer (86% vs 8%).
At worst, a leaking battery damage your device to the extent that it no longer works, if the leaked electrolyte corrodes the contacts of the device. So that you know which batteries to watch out for if you're likely to store them in a device where they could go flat, our leakage test uncovers which batteries are most likely to leak. We discharge four of each disposable battery, store them, and then check each week for any signs of leakage. The image below shows batteries being put through our leakage test.
Our test found one brand of battery where several cells leaked after six weeks. Find out which in our batteries reviews.
Which batteries are best value for money?
As well as testing how long batteries last under different conditions, we calculate the cost per hour for each battery. The longer a battery lasts, the better value it is. This means our results will let you compare at a glance how much battery life you’ll get for your money.
You can use this, as well as the test score, to find the best battery to fit your budget.
Top-scoring batteries earn our Best Buy recommendation.
Should I buy them?
All of our tests contribute to a total test score. The higher the score, the better the battery did in our tests.
Certain assessments are more important than others and so carry different weights. We think the most important job of a battery is to power your devices for the longest, so a large proportion of our total test score is based on this. Our overall ratings ignore price and are based on:
- 35% high-drain life
- 30% energy
- 25% medium-drain life
- 10% low-drain life
Top-scoring batteries with scores that stand out earn our Best Buy recommendation. Disposable batteries that score 40% or less are highlighted as Don’t Buy batteries to avoid.
Want to find out which batteries topped our tests? Go straight to Best Buy batteries.