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Is a batteries resting voltage a measure of it's charge?

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Old January 8th, 2012, 12:58   #1
Rusty Lugnuts
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Is a batteries resting voltage a measure of it's charge?

Hi How do you tell if a battery is fully charged? Can you tell by measuring anything with a normal multimeter? thanks for your help.
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Old January 8th, 2012, 14:37   #2
m102404
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yes and no. It's an indicator but not a wholy reliable one.

Look up the max voltage for your cell (i.e. 2/3A or sub-C or lipo)...then multiply by the number of cells in your pack.

However...there's plenty of times with a "so-so" battery that it'll be "charged up" but then die really quickly once in use. So while it charges "ok" it doesn't work.

What you'll want then is a smart charger that can display how many mAh it's putting into the battery....run that pack on a discharge and charge cycle and see if it's taking all the mAh that it's supposed to (or close to). Then use it and note how many cycles you get out of it (it'll depend on your setup). Then you'll know for sure if you are heading out with a good battery pack.

PS. I don't bother with that...I just buy quality batteries, charge them with a good smart charger, and have a spare quality battery as a backup.
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Old January 8th, 2012, 19:19   #3
ILLusion
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You can monitor a charge manually, but it takes a whole lot of babysitting and waiting for hours to see the charge voltage drop a few tenths of a volt.

Personally, it's worth my time to just invest in a smart charger to do the monitoring for me. Set it and forget it.

Measuring supposed cell voltage times the number is inaccurate, as Ni-Cad and Ni-MH cells are rated at 1.2volts per cell, yet can carry an actual potential difference between 1.25 and 1.35 volts. The value will depend on the age and condition of the cell. That means a rated 8.4v pack can have a fully charged resting voltage of anywhere from 8.75v to 9.45v... and you don't actually know what the FULL charge is, unless you've monitored the peak state during charge. When it comes off the charger, the voltage will be even higher - over 10 bolts (fully charged cells hot off a charger can show over 1.45volts.)

Save yourself some headache. Get a smart charger.

Last edited by ILLusion; January 8th, 2012 at 19:23..
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Old January 8th, 2012, 22:09   #4
Rusty Lugnuts
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Got one, it's a TLP model3000 -it's got a cooling fan, current adjustment. Heck i don't know what its doing at any given time,and i'm not sure how to use it or if it's working correctly. What i want is one with some indication whether its discharging or charging & if charging how much is it charging ,how close to done it is would be nice or at least something that indicates that it is done when it's done. SO my new question is any suggestions for a smart charger?
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Old January 9th, 2012, 22:19   #5
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iMAX B6, inexpensive, good quality, even does LiPo and lead acid batteries
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Old January 10th, 2012, 01:26   #6
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iMAX B6 or Turnigy Accucel-6 (or Accucel-8)

or pretty much any charger you see on Hobbyking.
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