I found a neat rechargeable 1200mAh  battery for testing at Walmart (it’s meant for an RC car that shoots BB’s) for about $20 with charger; it’s a 6-cell 7.2v Ni-MH unit that takes 4 hours to recharge.

I added a way to measure the battery voltage so Sniffer stops posting entries to the SD card before it’s little brain scrambles the data.

It ran for 15 hours.