Upvote:4
Your visa can be used throughout its validity period, unless cancelled or revoked. Hence you will be able to enter the USA on your current B-1/B-2 visa since it is hasn't expired yet. Moreover, the visa remains valid until it expires (ha, nice tautology). This is true regardless if it is contained in an invalid/expired passport. All you need to do is make sure you bring both passports when seeking admission into the USA. Finally, as IKeelYou suggests you should make sure that the visa page in the old passport is not damaged, to avoid any problems. Quoting from the US Department of State - Bureau of Consular Affairs website:
Additional Information
[...]
- Unless canceled or revoked, a visa is valid until its expiration date. Therefore, a valid U.S. visa in an expired passport is still valid. If you have a valid visa in your expired passport, do not remove it from your expired passport. You may use your valid visa in your expired passport along with a new valid passport for travel and admission to the United States.
The length of your stay is decided by the immigration officer who lets you in the country. The maximum allowed stay on a B-1/B-2 visa is 6 months.