Ok sure.
i'll try to make up some random values.
Let's say a connection from your phone to Google is 1 unit of battery. Lets also say that downloading 1 email is also 1 unit of battery.
Ok so, lets pretend you received 10 emails in 24 hours.
When you receive an email at gmail.com, if you have push set up, gmail.com sends a signal to your phone which established a connection (1 unit) and tells it to download the email (1 unit). For 10 emails, that's 20 units in 24 hours.
When you set it to sync every hour and check for emails (each sync establishing a connection), that's already 24 units. Plus another 10 units to download each email. 34 units if syncing every hour.
If its every 15 minutes, that's 106 units...
If you receive no emails, push uses no units. Sync uses 1 unit per scheduled sync.