Battery and alternator aren’t connecting right. What do I do?

What is your question?

The car will take a charge and can drive a few miles then speedometer will no longer read which makes me aware that the battery is losing its charge. The battery is new and had the alternator checked and it’s still good. What else could be the problem? Just replaced transmission with a used transmission

What makes this problem better or worse?

Driving

How long has your 1999 Volvo S80 had this problem?

About 3 days after changing transmission