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Author Topic: Anybody Know Why Rechargeables Fail Suddenly Like They Do?  (Read 1733 times)

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stevetoney

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Anybody Know Why Rechargeables Fail Suddenly Like They Do?
« on: February 19, 2014, 12:45:10 PM »
I'm pretty religious about keeping all of my batteries properly stored and charged up, though I don't keep my SLAs on trickle.  3 or 4 years ago, I picked up half a dozen 7.2V Ni-Mh batteries that have been some of my 'old faithful' goto batts since.  I've used them to death, so I knew they were probably getting close to giving up to the ghost.  So I wasn't surprised when two of them suddenly died...went from powering my gear for hours to not powering it for even ten seconds. 

What I don't really understand is that these batteries seemed to work pretty much like they did on Day One up until the day they wouldn't work.  I still have 4 out of the six that are still working and they still take the same amount of mah to fully charge them and seem to give me back the same amount of juice that they gave back on Day 1. 

Just wondering if anyone can explain why rechargeables seem to just fail suddenly on old age like they do.  You'd think there would be some indication that they're wearing out...shorter run times or whatever.

Is it because it's not about failure to deliver as many mah's which result in shorter run times but that degradation results in lower voltage so that it might not be enough to power your gear?   
« Last Edit: February 19, 2014, 12:52:01 PM by tonedeaf »

Offline Gutbucket

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Re: Anybody Know Why Rechargeables Fail Suddenly Like They Do?
« Reply #1 on: February 19, 2014, 01:08:07 PM »
Internal resistance goes up as they age.  I think that is a big part of what eventually causes problems, even if the voltage still measures OK.  One thing to remember if using a voltmeter to check for good battery voltage- measure while the battery is under load in the circuit, and not the open circuit voltage with a meter across the terminals and the battery unloaded.  While under load the voltage of a battery at the end of it's useable life will drop significantly, but still measure okay out of the circuit.

A good charger with various modes that can measure the battery's actual capacity (by doing a few discharge and recharge cycles and reporting on the actual discharged power) and/or recondition older batteries and report their true remaining capacity helps manage them.  I bought a better Maha charger after I had a few well-used but reliable NiMH die suddenly and/or refuse to run certain gear for more than a few minutes while running other gear for normal times (which I think had something to do with the internal resistance going up).  That charger let me condition new batteries initially for best performance, match them in pairs by their true tested capacities, and monitor/recondition/discard them whenever I grow suspect of them or have a battery problem.
« Last Edit: February 19, 2014, 03:09:05 PM by Gutbucket »
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stevetoney

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Re: Anybody Know Why Rechargeables Fail Suddenly Like They Do?
« Reply #2 on: February 19, 2014, 02:48:48 PM »
Thanks gutbucket.  Your comment about checking under load makes good sense.  I hadn't thought about doing that. 

Your Maha charger is just for AAs correct?  Wonder if there's charger that has comparable features that's a universal charger because I've grown to absolutely love my universal battery charger.

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Re: Anybody Know Why Rechargeables Fail Suddenly Like They Do?
« Reply #3 on: February 19, 2014, 03:34:31 PM »
It's the Maha MH-C9000 which accommodates up to four AA or AAAs.  I use a different Maha charger specificly for charging their 9.6V NiMH batteries.  And another make for 12v lead-acids.

Here it is at Thomas Distributing- http://www.thomasdistributing.com/Maha-MH-C9000-Advanced-Battery-Charger_p_2558.html

It's not inexpensive but has taken most of the worry out of managing rechargable AAs for me, and it runs off a 12v supply so I can use it in a car from a cigarette lighter or while primative camping from a 12v deep cycle battery.

The other suggestion is to use Low Self Discharge NiMH batteries.  Their capacity is only slightly less nominally than standard NiMH, but I find it about the same in practice.  Yet in my experience they are more reliable with a longer usable life-span in addition to holding their charge for much longer than standard NiMH will- more on par with the charge retention of alkaline cells.  Partly for those reasons I suspect they will 'die more gracefully' than standard NiMH when they eventually wear out as well.
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
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stevetoney

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Re: Anybody Know Why Rechargeables Fail Suddenly Like They Do?
« Reply #4 on: February 19, 2014, 04:11:01 PM »
Thanks for the link.  I'm familiar with that charger.  I do use AAs, so I've been meaning to get one of those chargers for years now.  But I'm at least as reliant on 6V and 12V SLA and 7.2V RC batteries.  I've been using a wonderful charger for charging those batteries called an Imax B6 (see link below), but it doesn't have the diagnostic and smart resurrection capabilities of the maha charger.  I've been looking for something like that for NiMH RC batteries.  I've found something for SLAs.

http://www.ebay.com/itm/iMAX-B6-Digital-LCD-RC-Lipo-NiMh-Battery-Balance-Charger-US-Delivery-/201038549205?pt=Radio_Control_Parts_Accessories&hash=item2eced4d0d5#ht_3406wt_1362

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Re: Anybody Know Why Rechargeables Fail Suddenly Like They Do?
« Reply #5 on: February 19, 2014, 04:54:32 PM »
Interesting.  I don't have any 6V SLAs or 7.2V RCs.  The charger I use on my 12V SLAs and a deep cycle boat battery is a 110VAC wall-transformer based 12V intellegent trickle charger designed for boat/car storage.  The other batteries I have all have internal charging circuits and state of charge indicators (a couple Eveready 5/9/12/18V and a number of 9V DVD lithiums) so those just need the right DC voltage injected into them.
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

 

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