What’s happening to you isn’t normal, so you’re going to want to find the cause, whether it’s a parasitic drain or a bad battery.
If storing a car for weeks at a time is a normal occurrence for you, you might consider getting one of these: https://www.amazon.com/gp/product/B0108JUWLY/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
I use one on my car’s dashboard (running a cable out the passenger door and under the hood, connected directly to the battery), and it gets enough sunlight through the windshield to keep the battery in my 1998 Honda Civic charged. One nice thing about this style of solar charger is that you can get an accessory-plug-to-USB adapter and use it to charge your cell phone when the power is out.