05 XC70 changed starter out and hooked battery back up, have lost radio code that I had when I bought car because they had to replace battery when I bought it. pusher power button on radio and got "power saving mode" on screen. My 99 v70 comes up with code when I change battery in it or charge it up after it sits a long time.

 

Two different issues. 1) - No Code. 2) low battery.
Your message indicate the latter. Once fixed, you will have the code problem.

You have either a bad battery or didn't tighten your terminal clamps or a bad cable .
First, how old is the battery? 3 YO or more ,just change it NOW.
Next, remove terminal clamps and inspect where the cable meet the clamp. Look for corrosion, and inspect the visable cable for swelling or weak spot allowing flex.
Clean clamps and battery posts, replace clamps on battery posts.

that'll clear the message. Next, go pay a dealer for your code, write it down and keep it in at least 2 locations (taped to inner glove box, car manual, and wherever you keep all your 'puter passwords would cover it)