New-Seeking Advice - to fix or not to fix

Hi. New member here. I have a 2004 Prius with 156,000 miles on it. I inherited it from my parents, who only put 45,000 miles on it, so I've never had to replace the main battery. But that warning light's come on, I'm taking her to the shop and after reading on this site expect to hear that one of the cells on the 12V battery has gone bad. This car has been so reliable. It's required very little maintenance so far. I think it may be worth replacing the battery with a refurbished and doing some body work I've put off. But it's going to cost a few thousand dollars. Opinions very welcome.