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  #1  
Old 12-06-2013, 7:31 AM
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the86d the86d is offline
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Default Lithium Ion Battery protection, Undervoltage?

In looking at some more Lithium Ion protected batteries they have a high and low voltage cutoff to prevent an explosion via venting gas (in an enclosed battery) compartment on overcharge for one.

1) When low voltage cut-off (2.73.0 V/cell?) is reached and if the battery discharges at an AVG of say 5%-10%/month, after 2 months the battery will not be chargeable any longer, or do they have circuitry like a diode that allows them to be charged when well under min voltage, or will the battery be EOL'd (w/typical charger)?

2) Does anyone have experience with a few different brands of 18650's, and know brands to avoid, or have some that you prefer? Some that don't seem to fit some devices due to a larger protected board at the bottom?
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Old 12-06-2013, 8:37 AM
CalLongGunner CalLongGunner is offline
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Quote:
Originally Posted by the86d View Post
In looking at some more Lithium Ion protected batteries they have a high and low voltage cutoff to prevent an explosion via venting gas (in an enclosed battery) compartment on overcharge for one.

1) When low voltage cut-off (2.73.0 V/cell?) is reached and if the battery discharges at an AVG of say 5%-10%/month, after 2 months the battery will not be chargeable any longer, or do they have circuitry like a diode that allows them to be charged when well under min voltage, or will the battery be EOL'd (w/typical charger)?

2) Does anyone have experience with a few different brands of 18650's, and know brands to avoid, or have some that you prefer? Some that don't seem to fit some devices due to a larger protected board at the bottom?
Low voltage cut off is usually in the circuitry of the device (around 3.2V). High voltage cut off is usually in the circuitry of the charger (4.2V).

Some cells ,mainly 18650's, have an additional built-in cut off around 3.0V

Most chargers look for 3V or higher from the battery before charging so if you discharge a battery down to 3.2V, then discharge it or wait for it to drop below 3.0V, the charger won't see it due to the cell-level cutoff.

Newer cells that are below 3.0V can be charged with a non-smart charger or charger/analyzer to bring it up over 3.0V and it might come back. However, charging Li-on batteries that have been outside their voltage range is dangerous and the older the cell is and the lower it was discharged below 3.0V, the more damage is done by over discharging .
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Old 12-07-2013, 3:30 PM
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You might want to check out candlepowerforum's electronics section http://www.candlepowerforums.com/vb/...eries-Included . There's a lot of info on LI batteries including 18650s.

I have the AW and Eagletac 18650s, both are the 3100 MAH versions and I have no complaints with either. I got the Eagletac batteries because one of my flashlights couldn't use flat top batteries.
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Old 12-07-2013, 3:44 PM
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It depends on the battery pack. They have internal low voltage cutoff and some can't be restored without tearing the battery pack and de soldering the cutoff circuitry. I'm an EE and have been forced to do it, but I'm amazed that the cheaper packs WILL not charge if low voltage. This stuff is not rocket science, but the batteries will heat and potentially burn without the overvoltage and undervoltage safeguards.. but dang they should charge..

I guess I'm suggesting to research the battery pack you buy...
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