You're getting a surface charge reading from running the engine. You need to 1) get a battery charger and charge it to full, this may take a couple of days if it's at 1/4. 2) when you reinstall the battery, disconnect the negative cable when not in use or install a battery disconnect switch.
There are many things that will put a parasitic load on a battery, such as the CO2 detector, radio, TV, antenna , microwave ( all have little red lights or clocks on them).
Your first problem is that you're not truly getting your battery back to full. Use a good three stage charger for this.
Second you have parasitic draws. You can isolate me and pull the fuses, or simply leave the negative cable off so it can't drain down the battery.
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