How do i add, and link/sync, and additional / secondart checking account from a bank that is different than the current checking account?

Helping you add a second checking account in QuickBooks Online is my priority, jfletch81.

Here’s how:

1. Go to the Banking menu or Transactions menu.
2. Select Connect Account on the landing page, or select Add account or Link account if you've already created an account. 
3. Search for your bank. You can connect most banks, even small credit unions. Tip: If you can’t find your bank on the list but still want to add your transactions to QuickBooks Online, you can manually upload bank transactions from a CSV file.
4. Select Continue. Then enter the username and password you use for your bank's website in the pop-up window. It may take a few minutes to connect. You'll see onscreen instructions if your bank requires additional security steps.
5. Select the accounts you want to connect (savings, checking, or credit card) to QuickBooks. You should see all of your accounts tied to your financial institution and can connect as many as you need. 
6. For each account, select the account type from the dropdown. These are accounts currently on your chart of accounts.
7. Select the date range for the download. Some banks download the last 90 days of transactions, others go back as far as 24 months.
8. Hit Connect.

If you don't see the new bank in the drop-down menu, select + Add New. This creates a new account on your chart of accounts. Then, select Checking for the Detail type. Fill out the rest of the form. Finally, click Save and close.

To learn more about setting up parent, sub-accounts and connecting them to online banking, see the recommended articles below:

• About bank or credit card subaccount setup
• Create subaccounts in your chart of accounts in QuickBooks Online

If there's anything else that I can help you find in QuickBooks Online, leave me a comment below. I'll be happy to assist you further. Wishing you the best.