Electronic – Battery charge times


I thought of an idea recently, and I wanted to know if electrical engineers agreed with my theory.

I have a smartphone.
Recently I bought a power bank because I found my phone's battery not holding up long enough.

Now here is what I thought about while charging my power bank and my phone.

If both batteries (of my phone and powerbank) could in theory fill up 1 mAh/minute and both my phone and and the power bank are connected to the outlet, and are actively charging, I'm basically charging the two batteries at an effective 2 mAh/minute.

If both my phone and my battery pack could hold 1000 mAh, I could charge both half way to 500 mAh and still have an effective 1000 mAh at half the time it would take me to charge the phone alone.

So if I bought three banks then together with my phone I could get the same effective 1000 mAh in just a quarter of the time!

So if this works in theory: Why not divide the phone's battery into hundreds of separate banks to get hundreds of times the times the charge rate? What prevents this in practice?

small diagram

Best Answer

It doesn't work that way. One of these two issues will get you:

  1. You "spilt" the original batteries into smaller batteries, maintaining the overall battery capacity. The smaller batteries now have lower capacity and lower maximum allowed charging current. If a original battery can be charged at 1 mAh/minute, then a battery resulting from a 1:2 split could only be charged at ½ mAh/minute.

    With the batteries split to conserve overall capacity, a larger fraction of the whole volume would be taken up by interrconnects, so the overall battery pack would now be larger and a little heavier.

  2. You use more of the same size batteries. Each can now be charged at the original rate, but the battery pack has become proportionally heavier and larger.

    The cell phone maker has already picked a tradeoff between size and weight on one side and longevity of charge on the other. For the same battery technology, you can't cheat this tradeoff. By adding more batteries, you increase longevity of charge, but you can't get away from the proportionally larger size and weight of the resulting battery pack.

If it were really so simple, they'd be doing it.