Battery dropping from 60% to 20% in seconds

[Steve Swift]

My wife's S4 Mini had poor battery life, so I bought a replacement off Amazon UK. No better.
Yesterday, she went for a walk in our forest, and the phone rebooted itself in her pocket.
Here are the battery history details:

What might cause such a huge loss of power (and why might her phone reboot itself? It does this quite often)

 

[B. Diddy]

Was the old battery doing the exact same thing as this new battery? Did the battery graph look the same, with sudden unexplained drops?

 

[Steve Swift]

The old battery was certainly losing charge fast, but I didn't do any research before replacing the battery. But then the new battery seemed just as bad. I got confused as to which battery was the original one, and which the replacement, so I wrote "1" and "2" on the batteries. But I'm still unsure which one was the original. I think the replacement battery had a lower serial number than the original battery which came with the S4.

In the meantime, I've been back to the Amazon page where I got the battery. There are several customer reviews complaining of similar symptoms, particularly getting down to 20% then dropping down to zero in minutes.
There were three suppliers other than Amazon, and there was speculation that some of the batteries were not OEM. So, I bought another battery, making sure that I get a genuine Samsung battery this time.

By tomorrow, I'll have three batteries, and now I know where to look for the power graph, I can compare behaviours.

 

[B. Diddy]

A sudden dropoff on the battery graph suggests a dendrite, but this usually appears after a while, not in a new battery. Hopefully the genuine battery works normally!

 

[zocster]

Yes, genuine battery always perform better. It could also be the phone needs a factory reset once in a while, especially with a replacement battery.

Sent from mTalk on 950XL

 

[Wm7Long]

@Steve Swift - There may be no Wi-Fi available in the woods. Personally, I'd suggest turning it off, and leaving it off. It's pretty quick & easy to turn it back on when needed. No sense in making S4mini try to connect when it's not really needed or especially when it's not even available. Of course, that's up to you & wife. Also, so many awakenings without the screen even being on may indicate some detective work is needed to track down wake-locks, or whatever they're called. Good luck, hope you can solve the issue.

 

[Steve Swift]

We use the Glimpse app while walking in our local forest. My wife and I go different ways, then use Glimpse to join up for the return home. In some places, there's not even phone coverage, but elsewhere mobile data is necessary for the mapping. I tend to follow unmarked tracks. With Glimpse running, my wife can find me if I have a heart attack or stroke.

 

[Steve Swift]

Well, the new battery went down from 100% to 6% steadily, over 20 hours. Lithium batteries get better after a few charges, so this should get better. The phone used to last longer, but that was before GPS and Mobile data usage increased significantly.
I bought an Anker Astro E1 5200mAh portable (very) charger, and we should be fine with this.
A new phone would probably fix this, but it would be larger than the S4Mini, and more expense...