I got one of Rex’s USB meters that measure mWh when charging phone from USB power supply
I have a Galaxy S9 phone and an Anker 20,000 mAh USB power supply
Rex said that a phone’s lithium battery will have a longer lifetime if you never charge it above 80% or let it go below 30%. I wonder if that would also save USB power supply life when charging the phone?
I use about 50% of my phone battery per day. I could charge it back up to 100% at the end of the day and let it run down to 50% the next day, or I could do 80% and 30%. Would that save significant energy from the USB power supply?
I charged phone to 100%. Ran Gaia with the display on so maybe the load was constant. It took:
65.8 min to go from 100% to 80%
126.8 min to go from 80% to 50%
73.1 min to go from 50% to 30%
Then I charged it back up and recorded mWh:
2156 mWh to go from 30% to 50%
3305 mWh to go from 50% to 80%
2235 mWh to go from 80% to 100%
% is not linear with actual power consumed. 100% to 80% took 65.8 min. 50% to 30% took 73.1 min. Charging form 30% to 50% resulted in more minutes of run time than 80% to 100%. So I corrected for that – 2156 mWh * 65.8 / 73.1 = 1941 mWh to get the same amount of run time.
Using that correction, it took 5540 mWh to charge from 50% to 100%. 5246 mWh to go from corrected 30% to 80%. 5246 / 5540 = 0.95 – it saves 5% of power if you charge from 30% to 80% each day, vs charging from 50% to 100%.
So, bottom line, it doesn’t really make enough difference to worry about. But, it saves a little. When I’m charging phone, if I notice it’s above 80% I’ll turn it off, but don’t worry much. When it get’s to 100%, it will continue to trickle even though it’s not adding to the phone charge so turn it off then.
Aside – if you could possibly be in a survival situation, you should charge to 100%. Obviously.
