Hi @jp – I only install 2.5W or for a shady location I upgrade to 10W. Can you share the site that is publishing on, and can see how fast the power went down.
The non recharge batteries could work – but you need to do a lot more power calculations to understand how long they will work. 4 batteries (4*1.6V =6V) will work for a boost plugged into USB-C, or a special connector instead of the Li-Ion – but then you need (3 * 1.6V = 4.8V) … , and probably D cells better options
My first suggestion is for you to get a USB Power Pack and just recharge the internal Li-Ion – I purchased this option a 10AHr USB, “10000mAh Dual USB Portable Charger, ”
and with a USB C cable plugged it into the Mayfly 1.1 – that recharged the LiIon battery in 2 hours
See https://monitormywatershed.org/sites/TUCA_Mi03/ battery Voltage – from Oct 1st. With the change in season there was less solar its deep in a Redwood forest The voltage declned from 4.125V and to about3.83V. At 3.8V my software stops it from transmitting readings. I was on site Nov 8, and plugged in the USB Power pack at 11:30 and it fully charged the 4.4Ahr battery by 13:00 – 90minutes. Then I also upgraded the panel to a 10W panel.
This was the context of the system. I align the solar panel to SW, but there was a lot of trees at that aspect, and with winter the solar aspect was decreasing.
Though after the above I moved the solar panel to 15′ away, and then upgraded the 2.5W to 10W solar panel – which gets enough dappled ambient for an hour or so to boost the battery enough