Charging iPhone with UPS or Powerbank

There’s nothing wrong with using a power bank to charge a phone. The phone doesn’t know the difference between a power bank and an AC adapter; all it sees is the output voltage and current. And unlike AC adapters where the quality is very important, because AC adapters can be shoddily made and can present a real risk of injury to you or your phone, power banks have no AC to isolate from the DC output, so safety is less of a concern.

Yes, charge your phone overnight with optimized charging enabled; during the pause at 80% the battery will rest, as all power will come from the power source.

Here’s what a typical charge curve looks like with optimized charging (real screenshot from my phone):

Hello Incogitant007,

Apple has a great post on how to keep your battery health for as long as possible, here.

When it come to using powerbanks, using any reputable brand like Belkin wont compromise your battery.

Batteries are consumables; they lose a little capacity every time they are discharged, then recharged. On average this works out to about a 1% loss for every 25 “full charge cycles”. As one example, if you charge the phone overnight, every night (and that is what you should do; it is a best practice), it starts the day at 100%. If it drops to 20% by the end of the day before you charge it again overnight that counts as 0.8 full charge cycles (20% to 100%), or about 24 full charge cycles per month of use. For this example your battery capacity will lose about 1% per month. Of course, if the end-of-day level is higher than 20% the capacity loss will be a little less, and if it is lower than 20%, or you charge it during the day, the capacity loss will be higher.

The absolute best way to get maximum use on a charge, as well as slow the decline of battery capacity long term is to enable Optimized Battery Charging (Settings/Battery/Battery Health) and charge the device overnight, every night. The battery will fast charge to 80%, then pause. During the nighttime pause the phone will use mains power instead of battery power, allowing the battery to “rest”, and thus reducing the need to charge the battery quite as often. The phone will resume charging to reach 100% when you are ready to use your phone; it will “learn” your usage pattern. If you enable iCloud Backup (Settings/[your name]/iCloud - iCloud Backup) the phone will back up overnight also, assuring that you can never lose more than the current day’s updates. Here's more information→About Optimized Battery Charging on your iPhone - Apple Support

Once the capacity drops below 80%, or if there is a message in Battery Health that the battery is not meeting peak performance expectations, it’s time to change the battery→iPhone Battery Replacement - Official Apple Support

They're generally no better or worse than charging via a power adapter or any other source as long as the source is of adequate quality.

The value of an iPhone on the secondary market might depend on the condition of the battery, but it can be replaced. I'd consider one more valuable if the seller had recently had the battery replaced at an Apple Store than if it was carefully babied for a certain amount of time and the battery health is 95%. Not only would the battery be newer and have higher capacity, but the adhesive seal will have been replaced.

However, I don't really concern myself with the condition to maintain the value. That's kind of a losing proposition because by the time I'm ready to move on, I'll have used up my device and I the value will be minimal. I makes more sense to me to get the value of my device rather than trying to maintain it to any standard for any residual value.