Today' project... Powering a flasher with ryobi 18v battery. I used a battery adapter with male spade connector to easily attach the battery. And then i used a DC to DC step down voltage converter to adjust the voltage down to 13.1v, its adjustable to whatever you need. (Probably should have fuse on other end of the converter incase of short). Running some tests now, I am expecting longer run time on 4ah ryobi than the SLA, but all i need is 10-12 hours.. according to spec i should get 20+ hours. Easily recharged when i get home, just clip it in with the rest and grab a fresh one. Could even carry a spare and still be less weight. /
Couple notes-
Humminbirds have over voltage protection if something was to malfunction, i dont know if other units do or not.
I tried straight from the battery and none of my units (3 flashers and two graphs) would run at 20.5V (actual output of these batteries).
All parts can be found on ebay, total cost for my build was $18.
It does fit back in my bag with PLENTY of room to spare, as you can see I used the largest project box I thought would fit comfortably so it wouldnt overheat (the converter does produce heat!!). I have this flasher in a lowrance bag, which is tighter than a humminbird. With the humminbird and the other knockoff bag I have there was even more room. No issues with fitting at all.
Weight of 9ah SLA- 5.65lb.
Weight of 4ah Ryobi- 1.6lb.
Obviously its not economical to buy all of this and a battery, you are better off buying a 12v lithium from dakota or amped. But if you already have the batteries like I do, well you can do this and save some money vs buying the battery and charger.
Dewalt and milwaukee offer a converter that outputs 12v already.. ryobi does not.