Thanks JT! I will note that down so I can make some informed requests down at the shop. Any ideas on a rechargeable battery for this?
I use a DeWalt 5Ah 20 Volt nominal tool battery for my Goto system and to drive an 8" Noctua fan through a DC/DC converter to drop it down to 12V. Both draw very little current. After 4 or 5 viewing sessions I've typically used less than 2Ah. Note that power is the product of current and voltage so the current out of the battery to the fan running at 12V is a factor 12/20 of the current through the fan. You can find different Ah sizes with a charger on Ebay for a good price. Iirc I paid $60 for my 5Ah battery and a charger.
They last a long time, and no worries about sulphate buildup killing them when the sit unused for a long time as in lead acid batteries. I've been running the lithium batteries in the car I converted to electric for almost 11 years now, and that is a much more demanding application. You can get DC/DC converters in various form factors from Digikey or Mouser for cheap. I paid a bit more for one mounted with terminal screws ($20?) to make hooking it up easy.