2010 Cadillac CTS - Worried about battery

If I ever get the battery replaced in my car, its only 8 1/2 years old, you are free to come over and tip the guy (or girl). My car sat for 2 weeks before I got a Walmart grocery curbside pickup order and it started just fine. Not really worried, I have an almost 60 year old battery charger. So far, Walmart is the only place I can get free pickup to my car. Target has it too but it looks like you have to have a smart phone or tablet.