What is the battery indicator on your phone really telling you?

One of the things we have become accustomed to relying upon on our mobile devices is the little battery charge indicator. I am still surprised at the number of times I hear people say

my phone battery does not last as long as it used to, even when it is showing 100% charged!

So, what does ‘100%’ mean? On most devices the battery indicator that displays shows the relative state of charge. It has no relationship to the actual energy content of the battery. Each time you use the battery, the amount of charge it is capable of holding slightly reduces. The reduction will vary depending on many factors, such as how much of the charge in the battery you use between each recharge. Over the course of a year, a frequently used ‘phone battery may have lost 20% to 30% of its ability to store charge. But, the device state of charge indicator will still show 100% when it is ‘fully’ charged.

Another complaint I hear is that a device suddenly switches off even when it was showing that it had (for example) 30% charge remaining. This is a consequence of the same problem, the clever bits that calculate the state of charge of the battery need to know how big the energy reservoir is. The start point is known when new, but unless the state of charge indicator circuit is recalibrated, the accuracy of predicting the precise moment the battery will run out of charge will diminish. If the state of charge indicator always starts at 100%, even though the reservoir is 30% smaller the when new, it is inevitable that the device will suddenly loose battery power earlier than predicted.

Always check in the device user manual, there may be a routine it suggests going through to restore state of charge indicator accuracy. This normally involves cycling the battery between two known states of charge, normally from fully discharged back to being fully charged.

Although this will not give you any extra battery life, at least it will make predicting when it will no longer power the device more reliable. But, with a bit of extra knowledge, and some in use management, using the battery state of charge indicator can help give you more battery life. But that’s for another blog!

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