Do I need to do a back up of my contacts and photos before having the battery replaced?

You need to have everything either backed up or synced as often as necessary to avoid losing content if disaster strikes, not just before a repair. Disasters such as dropping a phone in a toilet (the single most common cause of phone damage), lost or stolen, thrown under a bus, and so on. Think “what data do I have on this phone that I would miss if I lost it right now?” That should determine how often to back it up. The same applies to your computer. If your computer died in the next 5 minutes, what do you have stored on it that you would kick yourself for losing?

If you turn on automatic backups on your iPhone, and charge the phone overnight, every night, you can never lose more than content that was updated on the day disaster struck. You should apply the same standard to your computer. If you have a Mac you can get an external drive and enable Time Machine, which will back up your Mac every hour, and keep each backup separate, so you can retrieve content from the past that was updated since. It’s built into the Mac. Windows out of the box doesn’t have this capability, but there are several 3rd party backup utilities for Windows that are similar.

It's a good practice to have everything backed up prior to having work done on your phone. If something goes wrong they may need to replace your phone or there could be complications where everything could be wiped off the device. It's not common but can happen.

It is always a good idea to have a current back up of your iPhone. This can be done either on ➔ iCloud or on a computer.

I have had batteries replaced by Apple on my previous iPhones and have never lost any data. However, anything can go wrong when the iPhone has to be opened and a component has to be replaced. To guard against this risk, I recommend that you backup your iPhone.

Axel F.