RDIGID 9AMP BATTERY TO 12V ADAPTER

[Kevin23]

Yes "most" power tool batteries have a controller that can shut the battery off when the voltage drops to a certain voltage WHEN it is connected to the tool it was designed for (drill, flashlight etc).
I am not aware of a power tool battery that will "shut" off if the voltage is just taken of the battery when not in a tool, there maybe one but I've not seen it.
As a mater of fact most Makita batteries if drawn down too far will NOT recharge and the battery controller will "set" the battery as bad. The charger thinks that one of the cells is bad, self preservation fire prevention.

My ryobi does. Already has on a flasher. So does my buddy's fuel which left hooked to LED lights and on all weekend once. Now drop the draw and you are screwed, I left a battery in an unplugged charger once for months and evidently it had a ghost draw... The lithium chargers would not recognize it, but luckily I had an old school nicad charger in the corner of the garage that gave it enough of a jump start.

FWIW all lithium batteries these days have the cutoff in them, any that we would use for this application. Maybe you are thinking of the over draw (heat) protection that the tool tells the battery? If it draws too much current it shuts the battery off to protect it from overheating.

[MT204]

My ryobi does. Already has on a flasher. So does my buddy's fuel which left hooked to LED lights and on all weekend once. Now drop the draw and you are screwed, I left a battery in an unplugged charger once for months and evidently it had a ghost draw... The lithium chargers would not recognize it, but luckily I had an old school nicad charger in the corner of the garage that gave it enough of a jump start.

FWIW all lithium batteries these days have the cutoff in them, any that we would use for this application. Maybe you are thinking of the over draw (heat) protection that the tool tells the battery? If it draws too much current it shuts the battery off to protect it from overheating.

Nope not thinking of the overheating/over current.
Know for a fact that Makita, Milwauke do not shut off they just go dead. In fact I tried a Makita this afternoon watched the voltage drop below 1 volt and battery was dead, almost couldn't get it charged again. I have also tried it with Milwaukee. So what voltage are the ones that you using shutting of at?

[badger132]

Not sure about getting more AH- I think you mean the Watt- Hours are constant- when you reduce the voltage, you get more amps, minus the loss in the converter. Just remember that the unit itself has a converter, from 12V (13.6 down to 9 or so) to 5 volts or less, whatever the board runs on. You are really not saving power by reducing the input voltage to 12V- you are just giving the internal DC/DC converter a lower voltage to work with, and more amp- it is really the same power from the battery (minus losses)
A battery has so much energy and that is volts X amps X hours, and if you convert down to 12 you have not made more power, you have just traded volts for amps, and lost a little in the conversion.

[MT204]

Not sure about getting more AH- I think you mean the Watt- Hours are constant- when you reduce the voltage, you get more amps, minus the loss in the converter. Just remember that the unit itself has a converter, from 12V (13.6 down to 9 or so) to 5 volts or less, whatever the board runs on. You are really not saving power by reducing the input voltage to 12V- you are just giving the internal DC/DC converter a lower voltage to work with, and more amp- it is really the same power from the battery (minus losses)
A battery has so much energy and that is volts X amps X hours, and if you convert down to 12 you have not made more power, you have just traded volts for amps, and lost a little in the conversion.

Exactly.
It's all Ohms law.
Batteries have only so much stored energy (as you said).
I have done some load testing with tool batteries and buck converters.
This is the tester that I have used for years, very accurate. http://www.westmountainradio.com/product_info.php?products_id=cba4.
Start with a battery (doesn't matter the type or voltage)  and set the buck converter output to say 12.5 volts with "X" amp load and check battery run time.
Same test with the buck converter output set to say 14 volts with the same "X" amp load and the run times will be for all intents the same, they may vary a bit but that could be battery recharging etc.
Another thing to remember is that most lithium-ion batteries have a minimum/maximum voltage that depends on the chemistry of the cell. Some batteries are now 4.35 volts per cell, times 5 cells (18/20 tool battery) equals 21.75 volts.
At the other end is the lowest battery voltage which it should never be "loaded" below. There again that depends on the chemistry as well. Generally the low voltage is about (depends on battery) 3 volts, so 3 volts x 5 cells equals 15 volts.
With the above tester the shut off voltage can be set so the tests are equal.
Like you said the load (fishing electronics) is only using "X" amps.
And as always your mileage may vary.

[kayl]

I know this is an old topic, but I recently did exactly what OP is asking about to power a USB port and led lights in my new flipover. 18v Ridgid adapter to 18v to 12v converter from Amazon. Easy as pie.