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Old Mar 21, 2012, 01:08 PM
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United States, IN, Merrillville
Joined Jan 2006
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Question
Battery drained overnight?

I have a new 6v 2200mah ni-mh "hi-energy" receiver battery.

Last night Charged it at .25 amp for 2hrs. (i thought it would take longer)
reading was 7.6v charged.

I left my charger unplugged... but accidentally left the battery connected to the charger.

In the morning.. battery read 6.4v.. and charger said battery was <30% charged.

Question... Does leaving your battery connected to a unplugged charger drain the battery? Or is this a bad battery that drained itself overnight?

edit: charger is "vision peak ultra"

Thanks
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Old Mar 21, 2012, 01:12 PM
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Most chargers will drain a battery if left connected to a charger with no power input. You have a lot of circuitry in there, and it takes power to run it. Just plug it in, and be sure to remove the battery before removing power Roy BTDT
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Old Mar 21, 2012, 01:17 PM
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Originally Posted by Mr. foambuilder View Post
Most chargers will drain a battery if left connected to a charger with no power input. You have a lot of circuitry in there, and it takes power to run it. Just plug it in, and be sure to remove the battery before removing power Roy BTDT
Ty for your response. It makes sense what you are saying. Although, with the battery connected, the charger did not light up. And my charger has no cycle feature. So maybe I could use this technique to cycle my batteries also?
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Old Mar 21, 2012, 02:14 PM
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Your battery is still connected to electronics in the charger which will discharge the battery over time. You should never leave batteries connected to anyhting for extended periods of time. Even batteries in your flashlights will not last as long when left in the flashlight as they will if you remove them.

Some will say there is no way a flashlight thats turned off will discharge a battery, but they will. Ever wonder why every time you go for a flashlight it doesn't shine like it should. It's because you left the batteries in it and they slowly discharge. Try keeping your batteries out of your flashlights and see how long they last.
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Old Mar 21, 2012, 02:35 PM
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Another problem was that the battery almost certainly was nowhere near fully charged after only 2 hours at that rate.
A 250mAh charge rate is just a tad over 1/10C, so you'd need to leave it on at that rate for better than 14 hours to be fully charged. That 7.6V reading was most likely just a surface charge, especially if you weren't using a voltmeter that provided a load. Try a good formation charge over-nite and see how the capacity increases.
Pete
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Old Mar 21, 2012, 02:43 PM
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Originally Posted by pilotpete2 View Post
Another problem was that the battery almost certainly was nowhere near fully charged after only 2 hours at that rate.
A 250mAh charge rate is just a tad over 1/10C, so you'd need to leave it on at that rate for better than 14 hours to be fully charged. That 7.6V reading was most likely just a surface charge, especially if you weren't using a voltmeter that provided a load. Try a good formation charge over-nite and see how the capacity increases.
Pete
Wow Pete. this really is informative. TY.
I am in the market for a better charger. But currently this one does not measure with a load.

After 2 hours my charger beeped and showed 4 bars (like a cellphone) fully charged. After it beeps, all it does is trickle charge. So im a bit confused why my charger said it was fully charged

also, what do you mean "good formation charge"
Does that mean try to charge it at 1c? or something?
Or should I just leave it to trickle all night?
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Old Mar 21, 2012, 03:02 PM
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For original poster ..... it is worth knowing that a NiCD or NiMH battery will show good voltage right up until just before its flat.

The discharge curve of a rechargeable battery is near flat and is why they are much better than dry-cells. Initially a dry-cell shows 1.5V but under load it is significantly less often below 1.2V and falls of at a steady rate as it discharges. A rechargeable cell, even though it initially shows 1.25 - 1.3V is far more able to sustain its voltage under load and has a flat discharge ...

When charging a NiMH or NiCD ... with only a small amount of charge - you will see a voltage that without sophisticated good measuring meter will appear full charge. You must charge for full period to be sure it's actually charged.
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Old Mar 21, 2012, 04:09 PM
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To put it bluntly, unloaded voltage (pure voltage reading) is almost completely worthless for determining the capacity stage of an NiXX battery.
The only reliable way to do that is a 1/5C monitored discharge from a battery known to be charged at 1/10C for 15 hours and rested for a bit.
You will lose up to 10% of an initial charge in the first 24 hours just sitting. That is completely normal.
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Old Mar 21, 2012, 05:21 PM
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Originally Posted by flydiver View Post
To put it bluntly, unloaded voltage (pure voltage reading) is almost completely worthless for determining the capacity stage of an NiXX battery.
The only reliable way to do that is a 1/5C monitored discharge from a battery known to be charged at 1/10C for 15 hours and rested for a bit.
You will lose up to 10% of an initial charge in the first 24 hours just sitting. That is completely normal.
Bluntly ................ isn''t that what I said .............. but of course you are wrong in one sense .............. IF battery is completly fully charged - then voltage reading is correct.
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Old Mar 21, 2012, 11:07 PM
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Originally Posted by solentlife View Post

When charging a NiMH or NiCD ... with only a small amount of charge - you will see a voltage that without sophisticated good measuring meter will appear full charge. You must charge for full period to be sure it's actually charged.
I guess this is my problem. My charger shuts off after it auto detects that the battery if fully charged. then it initiates a trickle charge. I could go into boost mode which fast charges the battery every minute. but I have not used that feature.

The only thing I can do is leave everything connected and let it trickle charge. Take battery to the field tomorrow. and have someone load test it.

or maybe I should try and charge at 2.2 amps and just see what it does...

and yes both of you are really correct in that.... I need a load tester
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Old Mar 22, 2012, 08:08 AM
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Originally Posted by unitoo1 View Post
I guess this is my problem. My charger shuts off after it auto detects that the battery if fully charged. then it initiates a trickle charge. I could go into boost mode which fast charges the battery every minute. but I have not used that feature.

The only thing I can do is leave everything connected and let it trickle charge. Take battery to the field tomorrow. and have someone load test it.

or maybe I should try and charge at 2.2 amps and just see what it does...

and yes both of you are really correct in that.... I need a load tester
Forget all about load testers and that kerfuffle .... here's the KISS way to do it.

Charge up on your auto detect charger. Let it charge and kick out to trickle charge. Disconnect and let battery rest for 15 mins or so.

Get a suitable voltage flashlight bulb ... one of those screwdriver test lamp thingees in tool-box is good. Now check time ... connect lamp ... keep checking back to see if light is fading .. when it starts to fade - disconnect noting time.


You can then work out the mA capacity ......... or just accept that if the lamp runs for a good time ... battery is fine ! A bad battery will run for very short time only and is usually very obvious.

This is best DIY way to check a battery / cycle one.
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Old Mar 22, 2012, 10:42 PM
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Originally Posted by solentlife View Post
Forget all about load testers and that kerfuffle .... here's the KISS way to do it.

Charge up on your auto detect charger. Let it charge and kick out to trickle charge. Disconnect and let battery rest for 15 mins or so.

Get a suitable voltage flashlight bulb ... one of those screwdriver test lamp thingees in tool-box is good. Now check time ... connect lamp ... keep checking back to see if light is fading .. when it starts to fade - disconnect noting time.


You can then work out the mA capacity ......... or just accept that if the lamp runs for a good time ... battery is fine ! A bad battery will run for very short time only and is usually very obvious.

This is best DIY way to check a battery / cycle one.

welp that is a pretty cool DIY! I have one of those testers around here someplace I will do it as an experiment. (because its fun) Although I do love gadgets. and a load tester is pretty cheap. I will do both

Update: I plugged up my discharged battery onto my charger again. .25 amp charge. and it took 2 hrs again. the same as before. But.... This time the battery was actually warm (a good thing) where last time it was not. (very weird) so I took it to the field and a buddy load tested. it tested good. 7.4v with load if i remember correct. So I guess all is good.

1) I now know that my charger (if unplugged) will discharge a connected battery pack. I will assume it might discharge battery to dangerous levels if left connected accidentally.

2) I now know a cool DIY tester. and that a load tester is valuable also.
either way, you need to test battery with something other than a cheaper charger. due to the chemistry of certain batteries.

Thanks guys !!
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Old Mar 23, 2012, 03:45 AM View Post
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