12V 7.5AH SLABS for $23.83 each in sporting goods next to the trail cams. I still use SLABs when on a budget, weight is not an issue, and charging arrangements are odd. Unlike more modern battery chemistries, SLABs are very tolerant when it comes to charging them in a field expedient manner.
My standard go-to these days for offline writing and diagramming. 97 cents each in the office/school supplies. USA made. Get one for the MONEX this week, and make it your first LP/lab notebook. Bring one to class.