Only sync photos to icloud when plugged in?

I noticed that on icloud.com, when i add a reminder, it automatically gets sync on my phone when i turn on my wifi. Which is great and i really love that feature.

But that got me thinking, are my photos being synced too? Wouldnt that consume lots of data uploading it and also the battery?

Also, since im already here, why cant i access photos on the icloud.com website? Only on the windows explorer