How Much Does Battery Health Matter?

Users on smartphone tech support forums are constantly worrying over battery health. It’s not uncommon to see posts worrying over measurements like 95-percent or higher. And that’s natural and understandable: battery health appears to be a clean and reliable indicator of how your battery is doing, and without a good battery, your phone is just a paperweight. But battery health is barely relevant to the health of your device and almost always wrong anyway.

What Is Battery Health?


Batteries are harder to measure than you might expect. Even something routine – measuring the battery’s current charge – produces significant errors and inaccuracies. Battery health is a rough approximation at best. Phones can only measure your battery capacity precisely to a point.

Worse still, the battery’s organic chemical makeup introduces organic errors that cannot be overcome. Your battery’s capacity might vary by a couple percentage points each time you charge it, sometimes as much as 10 percent. So any battery health measurement you see could miss the mark by as much as 10 percent.

Consider a concrete example. Imagine your battery had a brand-new capacity of 3000 mAh. Today, your battery holds 2880 mAh. Your phone reports this as “96% battery health” because your battery can now only hold 96 percent of the original capacity. Supposedly, this number approximates battery degradation and therefore battery status.

Does Battery Health Matter?


All batteries degrade. Chemical components break down, reactions slow, catalysts fizzle. On a long enough timeline, every battery will eventually lose enough capacity to fail. Nothing can escape the ravages of entropy. As a result, battery health will gradually decrease no matter how much you baby it. It’s both expected and unimportant.

Fortunately for us, today’s lithium-ion batteries last for ages before degrading a meaningful amount. For most people, your phone’s battery lasts longer than the device’s useful life. Battery health will gradually decrease over time as the battery decays, but this is both expected and normal. It’s not uncommon to sell or recycle a phone with 90-percent battery health after years of use.

So we have an inaccurate measurement that doesn’t tell us what it purports to while encouraging concern over a non-issue. Battery health isn’t completely irrelevant, but if battery health and irrelevancy were at a party together, battery health would be standing uncomfortably close.

In most cases, battery health tells you as much about the battery’s failure rate as the Dow Jone’s Industrial Average tells you about the nation’s economy. As any stockbroker will tell you, the Dow bears only a casual relationship to reality.

Basically, you can safely ignore any measurement of battery health above about 80 percent. Anything above 90 percent is perfect functionality. Only when your battery’s health gets low and stays low consistently should you be concerned. Anything consistently below roughly 80 percent is worth being examined.

Then What Should We Look At?

If we can’t use battery health to gauge a battery’s duration, what can we use?

The most reliable indicator of battery health will always be user experience. If you’re worried about your battery, keep an eye out for some classic signs of battery failure. Does your phone suddenly die with a 30-percent charge remaining? Do basic operations suddenly take twice as long? Those symptoms indicate battery problems reliably and accurately. Ironically, your phone might even indicate great battery health in the midst of these issues. And that alone tells you everything you need to know about battery health’s accuracy.

Alexander Fox
Alexander Fox

Alexander Fox is a tech and science writer based in Philadelphia, PA with one cat, three Macs and more USB cables than he could ever use.

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