So, you want to save some money in 2025 and buy a used iPhone 12 or 13? I completely get it. They look almost identical, and the prices are tempting.
But as someone who has been repairing phones for over a decade and has personally inspected thousands of devices, I have to tell you: This is a trap.
The “waters” for these two models in the used market are much deeper than you think. There’s a “hidden” hardware defect, a “time bomb” repair risk, and one massive difference that will define your entire experience.
Here’s the quick 150-word answer in case you’re in a hurry:
For most people, the used iPhone 13 is the better choice in 2025. Its battery life is significantly better (averaging 1.5 to 2.5 hours more), its screen is much brighter outdoors, and it will get at least one more year of software updates.
However, the iPhone 12 can be a decent budget option, only if you buy it from an absolutely reliable source and fully understand its specific hardware risks related to the battery and screen.
In this ultimate guide, I’ll use my 10+ years of teardown experience to take you far beyond the generic spec sheets.
We will dive deep into:
- The “Battery Health” Scam: Why a 100% healthy used battery is actually a red flag.
- The Hardware Pitfall Guide: The 12’s “Green Screen” vs. the 13’s “Pink Screen”—which one is the real deal-breaker?
- The “Unknown Part” Warning: How this warning can turn your Face ID repair into a nightmare.
After reading this, you’ll have an expert’s eye and will never buy the wrong phone.
Quick Comparison: The 2025 Used iPhone 12 vs 13 Ultimate Guide
Before we get into the technical details, here is the summary I would give a friend.
In 2025, your priority isn’t chasing split-second speed improvements. It’s battery life, durability, and risk avoidance.
This table summarizes everything you need to know:
| Feature/Consideration | Used iPhone 12 (2020) | Used iPhone 13 (2021) | The Expert’s Insight |
| Battery Life (Real-World) | Poor (Power bank required) | Good (Lasts a full day) | The 13 wins, period. This is the most important upgrade. |
| Screen (Outdoor Brightness) | 625 nits (Struggles in sun) | 800 nits (Clear in sun) | The 13 wins. A huge difference in daily use. |
| Performance (A14 vs A15) | 4-Core GPU | 5-Core GPU | No difference in daily use. The 13 is better for heavy gaming. |
| Apple AI Support | Not Supported | Not Supported | Neither can use the latest Apple Intelligence. |
| Camera (Stabilization) | Standard OIS | Sensor-Shift OIS | The 13’s video is steadier, and night shots are brighter. |
| Major Hardware Risk | High (“Green Screen” permanent defect) | Low (“Pink Screen” was fixed) | The 12 is a hardware lottery. |
| Est. End of Software Support | 2027 | 2028 | The 13 has one extra year of life. |
| 3rd-Party Repair Risk | Medium | High (Screen swap can easily break Face ID) | This is the key contradiction. |
Do you see the contradiction here?
The iPhone 13 is a better phone in almost every way. But ironically, the iPhone 12 is actually a safer choice for third-party repairs.
This makes your purchase channel critically important. We’ll break that down next.
The #1 Difference: Battery Life (And Why the 13 Annihilates the 12)
If you only remember one thing, remember this: The iPhone 13’s battery life is far superior to the iPhone 12’s.
To be blunt, the iPhone 12’s battery life was its biggest weakness, even when it was new.
The Data:
- iPhone 12 Battery Capacity: ~2815 mAh
- iPhone 13 Battery Capacity: ~3227 mAh
This isn’t just numbers. The 13’s battery is physically 15% larger than the 12’s.
That 15% capacity, combined with the more power-efficient A15 chip, gives the iPhone 13 an average of 1.5 to 2.5 more hours of screen-on time than the 12 when new.
But we’re talking about used phones, right? This is where my “special answer” comes in.
Battery degradation magnifies this gap.
Let’s do the math. These phones are 4-5 years old. Any original battery is unlikely to have a health level above 85%; most hover between 75%-83%.
Let’s be conservative and assume both phones have 80% battery health:
- Used 12 Usable Capacity: 2815 mAh × 80% = ~2252 mAh
- Used 13 Usable Capacity: 3227 mAh × 80% = ~2581 mAh
Do you see the result?
A used iPhone 12 at 80% health has an actual capacity (2252 mAh) that is even lower than a brand new iPhone 12 mini (2227 mAh)!
You are essentially using a “mini” battery inside a full-sized body.
The iPhone 13, even after degradation, still has a usable capacity of 2581 mAh, which is much closer to the 12’s original capacity and is still a “usable” battery.
Conclusion: A used iPhone 12 is a “must-carry-a-power-bank” phone. A used iPhone 13 will very likely “last until you get home from work.” This difference is massive.
Expert’s Warning: Used vs. “Refurbished” Batteries (The Biggest Pitfall)
Reading this, you might think, “Okay Klark, I get it. The 12’s battery stinks. No problem, I’ll just buy a cheap 12 and pay $30 to get a new battery, right?”
STOP. This is the single biggest and deepest trap in the 2025 used iPhone market.
You need to know about something called “Part Serialization.”
Starting with the iPhone XS series, Apple began to electronically “pair” the battery to the phone’s logic board.
If you (or any third-party repair shop) replace the battery—even if you use a 100% genuine Apple battery pulled from another iPhone—the phone will immediately recognize the “non-paired” part.
Your phone will then permanently display an “Important Battery Message” or “Unknown Part” warning.
Why the “Unknown Part” Warning is a Deal-Breaker
“Klark, it’s just a pop-up. I don’t care.”
You’re wrong. It’s not just a pop-up. It’s a “check engine light” that hides critical information.
When this warning appears, your iPhone permanently disables the “Battery Health” feature in Settings.
I’ll repeat that: You will never be able to see your battery health percentage again.
Now, think about the only reason you replaced the battery—wasn’t it to get back to 100% health? This warning makes you forever lose the ability to see that.
You are “flying blind.” You’ll never know if that new battery is at 100% or 90%. You won’t know if it’s defective or degrading rapidly. You’ve traded a “known bad” (your 80% old battery) for a “complete unknown.”
The Scammer’s Trick (And How Krser Handles It)
It gets worse.
Unscrupulous sellers know that you (the buyer) will check the battery health. So, they counterfeit the 100% health reading.
We see this constantly on repair forums: a buyer gets a used iPhone showing “100% Health,” but a background data query shows it has 1,000 charge cycles.
How is this done?
The seller uses a “black magic” technique: they pry open the original battery, remove the tiny “BMS” (Battery Management System) chip, and transplant it via soldering onto a brand-new, cheap, third-party battery.
This tricks the phone into thinking it’s still the original battery. It will not show a warning, and it will display 100% health.
But this reading is meaningless. You’ve bought a low-quality battery that will likely overheat, swell, or even become a safety hazard.
This is the “Wild West” of the used market.
It’s also why we founded Krser. We have one non-negotiable rule: Every device we sell must be fully functional, just like new.
A professional refurbishment process must include rigorous testing of battery health. At Krser, for example, any product with battery health below 80% is replaced with a new, high-quality battery. This is our basic promise to our customers.
We would never “transplant” or “hack” a BMS chip to fake battery health. We would rather tell you honestly that we have replaced the battery with a new, more durable one and provide our own warranty for it.
What you get from us is a fully functional phone, not a “half-finished” product with hidden problems.
2025 Performance: Is the A14 Chip “Good Enough”?
Alright, with the critical battery issue out of the way, let’s talk performance.
First, let’s be clear: The A14 Bionic chip in the iPhone 12 is still not a slow chip in 2025.
For 90% of daily use—scrolling social media, watching YouTube, using maps, replying to messages—the A14 is more than capable. You will not feel a difference between it and the A15.
The real difference is in the GPU (Graphics Processing Unit).
- iPhone 12 (A14) has a 4-core GPU.
- iPhone 13 (A15) has a 5-core GPU.
Who needs the A15’s 5th GPU core?
This extra core is for two types of people:
- Heavy Gamers: If you play Genshin Impact or Call of Duty Mobile, the A15’s 5-core GPU will provide smoother, more stable frame rates.
- Video Editors: If you edit 4K video on your phone, the A15 will be faster at rendering and exporting.
If you just play Candy Crush occasionally, the A14 is perfectly fine.
The “Apple Intelligence” Problem: Does the A15 Have an AI Advantage?
This is a key update for 2025. You might be thinking, “The A15 chip is newer, it must be able to run Apple’s latest AI features, right?”
The answer is: NO.
Apple’s latest, powerful on-device AI suite—“Apple Intelligence”—explicitly requires an A17 Pro chip or a newer M-series chip.
This is a huge “equalizer.”
One of the key reasons to buy a newer chip is to “future-proof” for new features. But in 2025, Apple’s biggest new feature (AI) cannot be used by either the iPhone 12 or the iPhone 13.
This means that from a software feature perspective, the 12 and 13 are now passengers in the same boat.
Your decision should be 100% based on the physical differences—battery, screen, and camera—not on a non-existent “AI chip” advantage.
Screen Deep-Dive: Why 800 Nits Beats 625 Nits
This is my personal favorite “hidden” upgrade and one that non-tech people easily overlook.
On a spec sheet, both phones have a “6.1-inch Super Retina XDR display.” Their resolution and contrast ratio are identical.
Indoors, they look exactly the same.
But the second you walk outside into the sunlight, the iPhone 13 is the undisputed winner.
Let’s explain “nits”: “Nits” are a measurement of brightness. You don’t need to worry about “peak brightness” (that 1200 nit figure is for HDR video, not daily use). You need to care about “Typical Max Brightness.”
- iPhone 12: 625 nits (Typical Max)
- iPhone 13: 800 nits (Typical Max)
What does this 28% increase mean?
625 nits, by 2025 standards, is not enough in direct sunlight. You’ll be squinting, shielding the screen with your hand, and desperately trying to find an angle where you can see the content.
800 nits is the difference between “comfortable use” and “struggling.” This brightness is enough to “overpower” most outdoor glare, allowing you to clearly see what’s on your screen while using maps, replying to a message, or framing a photo.
This isn’t a gimmick. This is a real, tangible upgrade that will affect your user experience every single day.
Camera Teardown: Sensor-Shift OIS vs. Standard OIS
When the 13 was released, many people said, “The camera is unchanged.” As a technician, I have to say: They were all wrong.
The iPhone 13 (base model) inherited the core technology from the previous, most expensive model: the iPhone 12 Pro Max. That tech is Sensor-Shift Optical Image Stabilization.
Let’s explain: OIS (Optical Image Stabilization) is designed to counteract your hand’s shaking to make photos and videos clearer.
- iPhone 12 (Standard OIS): When your hand shakes, it moves the tiny, lightweight lens. This works okay.
- iPhone 13 (Sensor-Shift OIS): When your hand shakes, it moves the entire image sensor (CMOS). This is a larger, heavier, more central component that “floats” on a platform.
What’s the point of “Sensor-Shift”?
This isn’t marketing jargon. A “floating” sensor is much stronger at stabilization. This gives you two huge, visible benefits:
- Steadier Videos: Sensor-Shift can make thousands of micro-adjustments per second. This means your “walk-and-talk” videos will have far less jitter and will look “silky smooth.”
- Better Night Photos: This is the key. Because the sensor is extremely stable, the camera shutter can stay open for longer (without blurring the shot).
Longer shutter time = more light captured.
Combine this with the fact that the iPhone 13’s sensor is also physically larger than the 12’s (capturing even more light), and you have a “1 + 1 > 2” combination.
Conclusion: The iPhone 13’s night photos will be noticeably brighter, sharper, and less noisy than the 12’s. This is a hardware-level victory.
Is “Cinematic Mode” Still a Gimmick in 2025?
Yes. 100%.
This was the iPhone 13’s “Portrait Mode for video” feature. Looking back in 2025, its limitations are very obvious:
- Poor Quality: It’s locked at 1080p 30fps. In today’s 4K world, this quality just doesn’t hold up.
- Clunky Algorithm: Its AI-powered “focus racking” is very abrupt and often makes mistakes.
Verdict: It’s a fun toy, but it should absolutely not be a reason to buy the 13. The real video upgrade on the 13 is the Sensor-Shift stabilization, not this.
Hardware Pitfall Guide: The 12’s “Green Screen” vs. 13’s “Pink Screen”
This is one of my most important “special answers.” Every generation of used phones has its “urban legends” and hidden “landmines.”
The 12 and 13 each have a famous screen problem. But the key is: one is a permanent hardware defect, and the other was a fixable software error.
This makes their risk in the used market completely different.
iPhone 12 Risk: The “Green Screen” Hardware Lottery
- What is it? A very common issue. When you are in a dark room and turn the iPhone 12’s brightness very low, the parts of the screen that should be pure black or dark gray will emit an ugly, uneven green glow.
- The Cause? Hardware defect. This is not a software bug. It was a quality control problem with the OLED panels Apple used that year. It’s a “hardware lottery.”
- Why is this fatal? Because all of Apple’s subsequent iOS updates failed to fix it. This proves it is a permanent hardware flaw.
- Conclusion: If you buy a used iPhone 12 in 2025, you are gambling. You might get a perfect screen, or you might get a “green screen” unit. And once you get one, you can never fix it.
iPhone 13 “Risk”: The “Pink Screen of Death” Software Bug
- What is it? A much rarer issue. Some users reported their iPhone 13 screen would suddenly flash pink and then crash and restart.
- The Cause? Software bug. This is the crucial part. Apple officially confirmed this was a software bug.
- How to fix it? Very simple. A force restart, or, more permanently, updating your iOS.
- Conclusion: The “pink screen” is not a problem in 2025. Any used 13 you buy will be on a system version that fixed this bug long ago.
My Expert Verdict: The “Green Screen” is a permanent hardware risk you must avoid at all costs. The “Pink Screen” was a minor software hiccup that has long been resolved.
For screen durability and reliability, the iPhone 13 is a much safer bet.
The Final Deadline: How Many Years of iOS Updates Are Left?
When you buy a used phone, you are also buying its “remaining lifespan.” That lifespan is determined by Apple’s software support (iOS updates).
Once Apple stops providing updates for your phone, banking apps and social media apps will gradually stop working. More importantly, you will no longer receive critical security patches.
Apple typically provides an industry-leading 7-8 years of support. Based on this history, we can make a very reliable prediction:
- iPhone 12 (A14): Released in 2020. Expected final major iOS update in Fall 2027.
- iPhone 13 (A15): Released in 2021. Expected final major iOS update in Fall 2028.
What does this mean for you in 2025?
It is 2025 right now.
- The iPhone 12 has approximately 2 years of full feature and security support left.
- The iPhone 13 has approximately 3 years of full feature and security support left.
That extra money you spend on the iPhone 13 is buying you an entire extra year of usable life.
That’s a 33% increase in value, and it’s a very smart “investment in the future.”
[CRITICALLY IMPORTANT] The “Unknown Part” Warning (And Why the 13’s Repair Risk is Higher)
Okay, this is the most complex but also the most central part of this guide. Please read it carefully.
So far, we’ve established that the iPhone 13 wins on battery, screen, camera, and software life. It’s just a better phone.
HOWEVER, the iPhone 13 has a “time bomb” that the iPhone 12 does not, which makes its repair risk much higher when you (or a bad repair shop) break it.
Remember “Part Serialization”? Apple pairs parts to the logic board.
- On the iPhone 12, Apple paired the: Battery, Screen, and Rear Camera.
- On the iPhone 13, Apple paired the: Battery, Screen, Rear Camera… and the TrueDepth Camera (Face ID)!
The “Face ID Time Bomb”: A Real-World Scenario
Let me show you how this nightmare happens:
- You buy a used iPhone 13. You love it.
- One day, you accidentally drop it, and the screen shatters.
- To save money, you go to a “XX Repair” kiosk at the mall.
- The technician tells you a “genuine screen” replacement is $120.
- He replaces it. The screen looks good. You pay and go home.
- The next day, you realize your Face ID no longer works. You restart, you reset… it just tells you, “A problem was detected with Face ID.”
You’ve been had.
This is because on the iPhone 13, the screen and Face ID are paired together. To “correctly” replace a 13’s screen, a technician must have advanced micro-soldering skills to transfer a tiny EEPROM chip (which stores the pairing info) from your old screen onto the new screen.
90% of mall kiosks do not have this skill or can’t be bothered to do it.
The result: Your Face ID is now permanently disabled by software. You can never use it to unlock your phone or make payments again.
And the irony? This does not happen on an iPhone 12. On an iPhone 12, you can swap the screen freely. At worst, you’ll get an “Unknown Part” display warning (which disables True Tone), but your Face ID will still work perfectly.
This is why, as a repair expert, I must tell you: The third-party repair risk for an iPhone 13 is far higher than for an iPhone 12.
How This Should Affect Your Buying Decision
This makes your purchase channel the most important factor of all.
This is why at Krser, our number one business policy is to prioritize sourcing and selling original, unrepaired devices.
We firmly believe that the best used phone is one that never had a major problem in the first place.
We would rather spend more to acquire a “Like New” (pristine) or “Excellent” (minor wear) original device that passes all our functional tests, where we might only need to replace the battery (the right way)…
…than sell you an iPhone 13 that we ourselves don’t know how many times it’s been “tinkered with,” one that might be hiding a Face ID “time bomb.”
The risk you take buying from a private seller is precisely the value that a professional organization like ours eliminates for you.
Klark’s Final Verdict: Which One Should You Actually Buy in 2025?
Alright, you’ve seen all the technical deep-dives and hidden traps. You now know the difference between a 12 and 13 better than 99% of used buyers.
Here is my final expert advice.
My Recommendation: Buy the iPhone 13 (But From a Trusted Source)
For 90% of people, the iPhone 13 is the undisputed winner in 2025.
The extra money it costs over the 12 isn’t “spent”—it’s an investment you are making in a tangibly better experience.
You are buying:
- ~2 hours of extra battery life: The biggest daily improvement.
- A screen that is actually readable in sunlight: No more being “blind” outdoors.
- Noticeably better night photos and steadier video.
- An entire extra year of software and security support.
- The peace of mind that you 100% will not get a “Green Screen” defect.
As for its one “weakness”—that Face ID repair risk—you can perfectly avoid it by purchasing from a professional, trusted, and warrantied refurbisher (like Krser).
So, Who Should Buy the iPhone 12?
The iPhone 12 is only for buyers on an extremely tight budget.
You should only buy it if:
- You find an “impossible to refuse” price that is significantly lower than the iPhone 13 (e.g., a $100+ price difference).
- You must buy it from a professional refurbisher who offers a clear warranty, and you must explicitly ask them: “Has this unit been tested for the ‘Green Screen’ issue?”
My strong personal advice: Do not buy an iPhone 12 from Facebook Marketplace, eBay, or any private seller in 2025. The risk of you getting a “Green Screen” or a “hacked” battery is just too high.
Conclusion: Your Choice is About Value, Not Price
In the end, this debate isn’t just “12 vs 13.”
It’s a choice between “a cheap, high-risk gadget” and “a smart, reliable investment.”
My final piece of advice is this: In 2025, pay as much attention to who you are buying from as you do to the phone itself.
A cheap phone from a random seller with a “green screen,” a terrible battery, and an “Unknown Part” warning isn’t a “deal.” It’s “e-waste.”
A device from a professional company, in “Like New” or “Excellent” condition, with a new battery properly installed, and a solid warranty—that is a true “partner” that will serve you well for years to come.
That’s what we do at Krser, and regardless of where you ultimately buy, that should be your standard.
Your Turn
Are you using an iPhone 12 or 13 in 2025? What’s your real-world battery health? Have you ever run into the “Green Screen” or “Unknown Part” issues?
Share your experience in the comments below. I’d love to hear your stories.
Further Reading Suggestions:
We hope this guide has been helpful to you. If you’re interested in phone maintenance or purchasing used devices, perhaps the following articles could also provide valuable information:
“9 Practical Tips to Extend Your iPhone’s Battery Life” This article will help you understand how to better maintain your phone’s battery and improve its performance.
“Phone Screen Cracked? DIY Replacement vs. Professional Repair – The Ultimate Cost Showdown” – Learning some basic problem-solving methods might save you time and repair costs.
We are committed to providing more practical electronics knowledge to help you better use and maintain your devices.
