Help! '61 C10 battery won't hold charge

[bigfunsixone]

Problem began a couple weeks ago. Hadn't driven it for a couple weeks due to some bad weather. Had to jump it, drove for forty minutes, stopped it and started and it fired up right away. Drove for a bit more that day and it had no more trouble starting. Four days later, same thing. Had to jump it, drove for over 30 minutes, fired right up after being shut off. Now about a week after that, jumped it, drove for 30, but had no charge after I shut it off and tried to start. Before all this, never had a problem. Choke is ****ed up so cold starts were always a pain, but the battery was never the issue. I'm hoping it's just the voltage regulator, but maybe the battery's bye-bye or the generator's junked. Any thoughts? Just bought a digital multimeter to learn how to do charge tests. I'm a total greenhorn in the garage.

Thanks.