|You must SAVE bios settings after you make changes. Both the date and time should be set to current values. |
"...verify the polarity is correct...."
The battery polarity must be correct - in most cases, you must see the + on top of the battery when it's correctly installed in it's socket.
If the battery is installed upside down, the bios will behave the same way it does when the battery is dead or not there at all.
In rare cases there may be corrosion in the battery socket, or on the underside of the contact that touches it's top, that results in the battery having a poor connection. That corrosion must be removed - try household vinegar on a Q-tip, and/or you may need to scrape it off.
"Make sure you did not bend a battery contact."
If the top contact is bent away from the battery, a better way to fix that is to remove the battery, bend the contact toward the bottom of the socket, install the battery. (It's more difficult to bend it a short distance when the battery is installed than to bend it a longer distance when it isn't, and the metal tends to move opposite the direction you have moved it - spring back - when you let go. )