battery ? for Guido or eo-Th In

glennster

Well-known Member
i have a lithium ion battery question for you guys, as you seem to be the go-to guys for home made doo-dads for electrical stuff. i have a video light for my movie camera that uses 7.3 volt lithium ion batteries. the manual says to store the batteries completely discharged. but it doesnt say the best way to discharge them. i dont want to leave the light on to drain the batteries as the light gets too hot if you leave it on too long. what is the best way to drain them? i was thinking maybe getting a 12v automotive bulb and hooking that up and let them slow discharge. any thoughts??
 
Never heard of draining li battery. Put them in camera and leave it on. Should do the trick. For what it's worth, there is a ton of info about batteries, one source counterdicts there. Hard to say what is right.
 
unfortunately, the camera will shut off after about 20 seconds of non activity. that is why i was looking form some way to drain them out of the camera.
 
Wow... in my 20 years of using Lithium Ion in everything from photography equipment to power tools, I have never seen a manufacturer recommend storing completely discharged. In fact, a lot of Lithium Ion makers recommend never draining them to zero.

Most everything I have read states to store in a cool place with about a 40-50% charge.
 
Hello gleenster,

If you have not transposed the number, 7.3V is an odd rating?
Individual lithium-ion cell usually are rated @ 3.6V or3.7V. Those are the voltages you store the battery at. Most lithium-ion packs have a built in voltage cut-off of 2.7 V. for each cell in the pack.
So if that is the case, even hough you read zero voltage, they actually have the 2.7 potential as I stated earlier.
You need to know what you have. If the manual stated to totally discharge them, just do so, they probably have the protective circuit. Totally discharging unprotected cells will degrade them substantially!

GUIDO.
 
To me it sounds like they have a major case of CYA. If there is no power then no possible smoke later. Heard another Tesla fried. Don't ya know they NEVER report anything about the gas cars that cook every day. Do they now?? Would you like to drain all of the power out of your cordless drill when you store it? By the way, at work our Motorola radio packs are that voltage. Lawyers and government really tick me off anymore.
 
Hello jeffcat,

NiCad's thrive when totally discharged. All other......read the manual,

GUIDO.
 
glennster,
I think it would be safe to discharge a battery at 5-10% it's rating. So lets say you have a 1000 ma-hr battery, discharging it at 5% would be draining it at 50 ma. Ohm's law. E=IR so R = E/I
R = 7.4v/.050 = 148 ohms. Discharging at 5% will take 20 hrs. Discharge it at 10% it will take 10 hrs.
 

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