Battery Problem; 3 different phones, same problem

Hi everyone,

I’m hoping someone with extensive knowledge of iPhones, iOS, or battery diagnostics can help me figure out what is causing this problem. I’m honestly running out of ideas, and I’d really appreciate some technical insight rather than just the usual battery-saving tips.

Over the past two months, I’ve been trying to switch from Android to an iPhone. Unfortunately, I’ve experienced almost exactly the same problem with four different refurbished iPhones.

My phone history:

My first phone was a refurbished iPhone 15 Plus. After using it for a while, it started getting noticeably warm and the battery began draining extremely quickly, even when I wasn’t using it. I returned it.

I then received another refurbished iPhone 15 Plus, but the same problem occurred. I eventually sent it back for repair, but the issue persisted.

After that, I decided to try a different seller and switched to a refurbished iPhone 16 Plus from Refurbished.nl/refurbed.nl. I specifically chose the option for a new battery, hoping this would finally solve the problem. Unfortunately, the exact same issue has returned.

What exactly happens?

The problem seems to occur in phases. Sometimes the phone works perfectly fine for an entire day. Then, usually later in the day or in the evening, it suddenly starts getting warm and losing battery percentage much faster than normal.

This continues even when the screen is off and the phone is sitting unused. For example, I’ve observed the battery dropping by more than 6% in around 30 minutes while the phone was idle, and the phone felt noticeably warm.

The warmth is mainly around the upper part of the back of the phone.

Things I’ve already tested:

Airplane Mode: the problem still occurs, and the phone still gets warm, although I’m not certain whether it is slightly less warm.

Using the phone without a case: no noticeable difference.

Using it at home with a good Wi-Fi connection: the problem still occurs.

Removing the SIM card: the phone initially seemed to behave normally and stayed cooler, but the issue later returned even after other tests, so I’m not convinced the SIM is the cause.

Monitoring battery usage and background activity in Settings.

Checking the battery condition on my previous iPhone. It reported normal battery health, although I understand that this doesn’t rule out every possible battery issue.

I’ve already repeated various battery and app tests many times, so I’m hoping to investigate something beyond the usual suggestions.

One detail that might be important:

My previous phone was a Samsung Galaxy A16. I transferred my data to my iPhone using Apple’s Move to iOS app. This included thousands of photos, a large WhatsApp history, messages, contacts, and call history.

The initial transfer took quite a while, and I believe Photos may still have been syncing afterward. I’m wondering whether something related to the transfer, iCloud Photos, background processes, a particular app, or some other software configuration could be responsible.

However, I don’t know whether a software issue could realistically explain the same symptoms across four different iPhones. I also don’t want to assume that the transfer is responsible without evidence.

My main questions are:

What could cause multiple different iPhones to develop almost identical overheating and battery-drain symptoms?

Could a transferred app, data migration issue, iCloud syncing, or a shared software configuration cause this?

Is there a way to distinguish a software-related problem from a hardware or battery problem without immediately buying another phone or repeatedly returning devices?

Are there any diagnostic logs, analytics reports, or specific settings that could help identify the actual cause?

What would be the most useful next test to perform, given that airplane mode and several other basic tests haven’t resolved the issue?

I’m currently using a refurbished iPhone 16 Plus with the new-battery option, and I really don’t want to return another phone without first understanding what might be happening.

I’d especially appreciate responses from people with experience in iOS diagnostics, iPhone repair, or troubleshooting recurring battery issues. If you have a theory, please explain what evidence would support it and how I could test it.

Thanks in advance!