We've all seen the stories now. Older batteries make iPhones slow down. Apple has introduced an update to their iOS software which slows down iPhones in order to save battery life.

We had a couple of questions about this.

How much does Apple slow down iPhones? At what stage does this slow-down start?

Benchmarks

We assumed that once a battery had reached 500 charging cycles, which is when an iPhone battery starts to deteriorate rapidly, the slow-down began. But when we ran Geek Bench – which is a cross platform benchmarking tool – we saw some startling results.

These GeekBench 4 results are from an iPhone 6, running iOS 11.2.1

We actually started with an iPhone which had 140 charging cycles. Then we tested it with a new battery, and then with a battery which had 900 charging cycles. This battery was so depleted that we needed to have the iPhone on charge during the test. We wondered if this would falsely boost the rating of this setup, but after seeing the benchmark scores, we’re not so sure.

Battery status:

0 charging cycles. Battery status:

140 charging cycles. Battery status:

900 charging cycles.

28% Slower?

The second result is the most controversial one for me. After just 140 charging cycles, which could happen after just 4 months usage, the iPhone is running at 28% slower than it does with a new battery. After 140 cycles there should be no issues with the battery supplying the phone with the correct amount of power. There should be no reason to clock down the iPhone. Is Apple really saying that the peak performance of the iPhone is only available for the first few days? After just 4 months the performance will drop by 28%.

How to prevent this

This "feature" is enabled by default in all iPhone 6, 6 Plus, 6s, 6s Plus, 7, 7 Plus and iPhone SE models. There is currently no way to turn it off, and it's unlikely that it will be possible to disable it in the future. Apple says that by slowing down your iPhone they prevent it from cutting out at random times. The only way to keep your iPhone running at top speed is to have a new battery in it. Replacing a battery every 4 months might seem like an unlikely thing to want to do, but if someone told you that you could have a 28% faster iPhone for just £69, would you be tempted? I know I would.

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