How do I maintain iPhone battery health at 80% for 3-4 years?

Batteries are consumable parts and they can't be managed as precisely as you hope. No two iPhones batteries will degrade at the same exact rate, but degrade ALL Lion batteries do. On average, you can expect about a 1% decline for every 50 charge cycles. Battery Health decline is not linear. It can remain steady for a while, then drop a few points rapidly. That is what your friend who has 225 cycles will ultimately see. They will surely see a fairly quick decline once the batteries health dips.

You can't babysit an iPhone Battery. And your Battery Health at 98% is completely in line with expected performance after 117 Cycles. On my iPhone 17 Pro Max, it's health dipped to 99% at onloy 47 cycles, but that's not in way concerning to me.

Things you should do:

1. Never fully run the battery down to 0% - it will prematurely age the battery.
2. Avoid running the phone below 20% - same reason.
3. Do, plug your phone in to charge when you go to bed at night and leave it on charge ALL night, EVERY night, with Optimized Battery Charging enabled.
4. Stop worrying about Battery Health. Your battery will continue to decline and that's normal, expected and unstoppable. So worrying about it is pointless.
5. Read this about when to charge your iPhone --> When to charge your iPhone or iPad - Apple Community
6. When the day comes that your Battery Health dips to 80% or lower, that's the day you pay Apple to replace the battery. You're a LOOOOOOOONG way from there, so again, stop worrying.

Prolong and Maximise Battery Performance and maintain Health of the Battery

The measure of battery health deterioration/drainage is subjective and can vary depending on individual usage patterns. There is no universal standard to determine whether the battery health deterioration/drainage is normal or abnormal because it heavily relies on how the battery is used and maintained.

Protect & Prolong the Life of your iPhone's Battery:

1. About the battery usage on your iPhone, iPad, and iPod touch ...
2. Batteries - Maximising Performance - Apple (IN)
3. iPhone Battery and Performance
4. About Charge Limit and Optimised Battery Charging on iPhone - Apple Support (IN)

• Find out what to do if Optimised Battery Charging doesn’t activate.
• Find out what to do if your device stops charging unexpectedly.
• Find out what to do if you think your battery is draining too quickly.
• Find out how to charge and maintain your iPhone battery.

Try to monitor Battery usage by iPhone Activity as shown below

What is shown under battery usage? Checking that would give you an indication of the usage behavior.

1. Background Activity
2. Notifications
3. Connected to Charger
4. Or any Other

Try some of these options too.

To prolong the life of your iPhone battery, you can follow these tips and best practices:

To prolong the life of your iPhone battery, you can follow these tips and best practices:

1. Optimize Battery Charging: Enable the "Optimized Battery Charging" feature on your iPhone. It helps reduce the wear on the battery by slowing down the battery aging process. You can find this option in Settings > Battery > Battery Health. About Optimized Battery Charging on your iPhone - Apple Support (IN)
2. Avoid Extreme Temperatures: Extreme temperatures, both hot and cold, can negatively impact your battery life. Avoid exposing your iPhone to excessive heat or cold, such as leaving it in direct sunlight or in a freezing car.If your iPhone or iPad gets too hot or too cold – Apple Support (UK)
3. Use Original Chargers and Cables: Always use Apple's original chargers and cables or certified third-party accessories. Low-quality chargers or cables can damage the battery and reduce its lifespan. Identify counterfeit or uncertified Lightning connector accessories - Apple Support (IN)
4. Avoid Draining the Battery to Zero: Charge it whenever the charge becomes lower than 20%. The rest is up to you when to charge. how long to charge, how often to charge, which adapter to use starting from 5W to 140W USB-C Power Adapter etc.
5. Optimize Display Settings: Adjust your display settings to optimize battery life. Lower the screen brightness, enable auto-brightness, and use shorter screen timeout durations. Adjust the display and text size on iPhone - Apple Support (IN)
6. Minimize Background App Refresh: Limit the number of apps allowed to refresh in the background. Go to Settings > General > Background App Refresh and disable it for apps that don't require real-time updates. Switch apps on your iPhone, iPad, or iPod touch - Apple Support (IN)

I would say:

• never ever let ur battery below 25%
• charge only to 80% (then stop it ) if u can
• Dont charge while playing heavy games

Because Li ion batteries are technically chemical reactions , never fully reverse one will help elongate the life.

Also, Li ion batteries dont like heat, charging gives heat, heavy processing gives heat. This will depreciate the battery faster.

Btw i am using iphone 16e , after 316 cycles my health level still 100%

but i have a concern my friends iphone 16 with same usage had 100 % BH with 225 cycles over 8 months

Your friend was extremely lucky. When the battery was new, it was actually at 103-104%. But, Apple would still display this as 100% in the battery settings on the iPhone.

So, while the battery might be expected to decline 3-4% over 6-8 months....and it did....the display still read as 100%. Your friend is now going to see a more normal decline rate on their battery.

Don't try to babysit the battery. It will not help, and will just make you miserable if you are checking the settings all the time. Batteries are chemical devices. No two are exactly the same. The battery is going to do what it is going to do. The only way to slow down battery decline is use the phone less.

If your battery drops to 80% in the first year, Apple will replace the battery free of charge.

98% after 117 cycles is not problematic. It actually not bad at all. Here’s a link to the user guide, read up on the battery section: iPhone User Guide - Apple Support

Ultimately, I’d recommend charging your phone when it needs it and quit expending energy worrying about it. I’m on my 4th or 5th phone (x2 if you count my wife’s). We keep them for quite a while. I’ve NEVER had to replace a battery.

See my previous post. Read the user guide. Make your decisions based on that. Comparing two phones is absolutely pointless, since it is highly likely you had different use patterns. Batteries are expendable commodities. That’s just the way it is.