Thursday, June 09, 2016

Power starvation

Isle of Wight Music Festival

Ever sat in a tent watching the battery on your phone or tablet die, with no mains power?

Such was my experience in Minehead last weekend. So I bought this:

RAVPower 26800mAh 3-Port 5.5A iSmart Output
Portable Charger Compact Power Bank External Battery Pack

It performed flawlessly, quickly recharging Clare's iPad, my Nexus 6 phone and my Nexus 10 tablet.

It then took around 14 hours overnight to recharge the Power Bank from empty, using the iPad's 5V 2.1A USB mains-charger.


Tablets charge at 5V 2.1A from a USB mains-charger while for phones it's 5V 1A.

You can charge a tablet from a 1A phone charger - but it takes twice as long; you can charge a phone from a 2.1A tablet charger - the extra current capacity makes no difference and can't be used by the phone - but it's perfectly safe.

My Nexus 6 phone has a 3220 mAh battery, my Nexus 10 tablet has a 9000 mAh battery while Clare's iPad 2 has a 6,944mAh battery.

At 1 amp you would predict that the phone would take just over three hours to charge, the iPad would take seven hours and the tablet 9 hours.

This is why it makes sense, tablet-wise, to invest in a 2.1 amp charger like this, rather than just reusing old phone chargers, so as to halve these times..

AmazonBasics Wall Charger with USB Outlet (2.1 Amp Output)


Due to various inefficiencies, you should multiply the device charging times above by up to an additional 50% (assuming you were charging from empty - but recall you are advised not to let the charge drop below 30% for long-term battery-health reasons).