Is it good or bad, credit wise, to have a balance of zero on a credit card? For a length of time?

As long as the account is being reported at paid as agreed and you have no late fees or other charges, then keeping a $0 balance does not hurt your score.

You will not get many points for the account history as you have not used it and it does not provide a pattern of your credit use and payment history.

You should use it every now and then and simply pay it off when the statement arrives. You need to keep the account open as it provides you with a line of credit and that is used to determine your debt utilization ratio. This is how much you owe compared to how much credit you have available.

The lower the ratio the better your score.

If you close the accounts, you will loose that available credit line and this will lower your debt utilization ratio.

I have provided a link for you to learn how credit works and what affects your scores from FICO

Hope this helps answer your question.

You need a quick and easy guide to how the fico score works go here

http://hubpages.com/hub/experianficoscore

You'll see a section about what parameters credit reports are based.

Good luck

Some places will close your account if you don't use the card for an extended period of time.