slow charging phone

Why Does It Take So Long To Charge My Battery?
Fifth in a Series

When you are in a hurry, everything seems to move in slow motion.  Morning traffic.  Brewing coffee. Powering up the battery in your charger or cell phone.

On the latter, it’s not your imagination.  If you start out with an empty battery, you’ll notice it charges fairly quickly up to 90%, then slows down dramatically.  Getting to 100% seems to take forever.  This is because most battery circuits are designed for trickle charging.  This means the last 10% charges slowly over a period of time.  If the battery starts out very low, it doesn’t like to get too full too quickly.

Trickle charging is not good for batteries, but there’s good news.  You don’t need to charge your battery to 100% anyway.  If you care about the battery’s life, charge it only to about 90% of capacity.  This will keep your battery from being too full yet give you all the power you need to operate your phone or device.  To maintain the 90%, remember to charge your battery frequently which is better for the life of the battery in the long run.

See all stories in this series here.

– Dr. John Zhu

About this Series:

Ask Dr. John

PowerStick has been designing and manufacturing portable power chargers at its Canadian manufacturing plant for over 10 years. During that time, this product category has been the focus of much publicity around safety and compliance. Some extreme cases involving batteries have caused fires in chargers and phones and prompted airlines to treat their conveyance with an abundance of caution.

As distributors and their representatives field more and more requests from their clients for portable charging devices, and in an effort to demystify battery and charger safety, we have asked Dr. John Zhu to pen a series of short, easy-to-understand tutorials to explain the how-tos and safety aspects of responsibly buying and selling these convenient and popular tech products.  Learn More>

About Dr. John Zhu:

John Zhu is director of engineering at Following graduation and teaching in one of China’s top universities, he was offered a visiting scholar position at University of Pennsylvania. After that, John joined PowerStick with responsibilities for all areas of engineering and technical product design. He was responsible for the original CES award-winning PowerStick Classic and every charger since. He has more than 10 patents to his name and is highly regarded in his field.

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