1. Android Central Question's Avatar
    I've had my Samsung J7 since 2017. I am on it about 4-5 hours a day, and I wish I could use more of it, however, there's been a problem surfacing on it since February/Early March that I simply cannot get around.

    Lately, I'll be in the middle of using the phone, and it will claim it's at 70-80% after like 20 minutes, and it will shut down immediately as if the battery was dead. When I take out the battery for a minute or so and put it back in, it claims it's at around 4%. Now here's where it gets confusing.

    My roommate has a phone (another Samsung J7) and decided to mess around and switch the batteries and see what would happen. She turned on her phone, and the battery percentage said 68%, and she was able to easily use the phone. But when I turned on mine, it said it was at 7%. She had completely charged her phone the night before.

    How do I fix this? I don't understand why my phone is not reading the battery correctly, and even more importantly, why it can't be out of the charger for more than 20 minutes. Can someone help?
    07-05-2020 01:05 PM
  2. Mooncatt's Avatar
    Sounds like the battery is just worn out and voltage sag is affecting it more than normal.

    Any time you put a load on an electrical system, the voltage will temporarily dip. This is normal and happens on any electrical system. Ever had an air conditioner turn on and notice the lights dim? That's voltage sag.

    As a battery ages, internal resistance increases and voltage sag becomes more noticeable. When it's bad enough, you get the symptoms you describe. The battery may read a good charge to start out. If you do something intensive on it (I.e. gaming), the voltage will drop below the cutoff point and the phone instantly shuts off. When you turn it back on, it reads low because it's slow to recover the voltage and the bootup process is rather processor intensive.

    The only way to fix this is to replace the battery. That phone is getting up there in age, so it'll be a bit of a gamble to find a good one. Any new battery runs the risk of being old stock and already suffering capacity loss. Your best best would be direct from Samsung if possible.
    Laura Knotek likes this.
    07-05-2020 02:29 PM
  3. mustang7757's Avatar
    I'll leave a Link to register so you can communicate here as a guest account you can only post questions but can't reply
    07-05-2020 04:50 PM
  4. B. Diddy's Avatar
    Welcome to Android Central! Does this behavior persist in Safe Mode? https://www.t-mobile.com/support/dev...sung-galaxy-j7
    07-05-2020 08:21 PM

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