I've looked into some other possible options for extending the battery life of the audiomoth. Connecting an 8 cell battery holder in parallel with the existing battery pack would provide as much extra charge as a standard power bank if you filled it with eneloop pro rechargable batteries (2500 mAh per AA battery). The issue I anticipate there is that the original battery holder (3 AA batteries, ~4.5V) and the additional battery holder (8 AA batteries, ~12V) would have different voltages. If necessary, you could remove the original battery holder. Maybe even replace it with a second 8 cell battery holder to get an even longer life? https://shopee.sg/%E2%98%80Plastic-8-X-1.5V-AA-2A-CELL-Battery-Holder-12V-With-Lead-Wire-i.102279399.2232330557 https://shopee.sg/-2019-Eneloop-Pro-AA-4pcs-Rechargeable-Battery-Panasonic-Made-in-Japan-i.16194072.272172741

Ok, so I just need a power source that won't go to sleep? I've looked into powerbanks with "always on" features, but there are only a few models and they tend to be more expensive for less charge. Voltaic's V15, V50, V75 and V88 all have this feature. They can be used for long deployments of low power draw devices. https://voltaicsystems.com/always-on-batteries/ https://voltaicsystems.com/v15/ Another forum post mentioned using LiPo batteries, which seems like a good option except that the total mAh of LiPo batteries tends to be much lower than a standard power bank, so attaching one of those wouldn't necessarily give me the deployment duration I need. https://coolcomponents.co.uk/products/lithium-polymer-battery-2000mah