https://www.amazon.com/dp/B01NAJ3KQB https://www.amazon.com/dp/B01NAJ3KQB ...probably at least 10-25 hours playback on a single battery, which means 8 batterie

https://www.amazon.com/dp/B01NAJ3KQB https://www.amazon.com/dp/B01NAJ3KQB ...probably at least 10-25 hours playback on a single battery, which means 8 batteries gives you 80 hours of listening (2 weeks). For that space though, you could scavenge a solar garden light charger and get indefinite listening with ~4 batteries. 1 loaded, 3 charging, with a nominal "fully charge 3 batteries with 16 hours of daylight", which means a ~33% duty cycle. One sunny day charges 3 batteries, which means you have 45 hours of charge before needing to obtain another 16 hours of sunlight.