When to discharge NIMH

[nwiscan]

Hi I am new to recharables. I picked up a LaCross 700 and an assortment of AA's. Ive been just using the recharge function each time the radio I use them in alerts me to a low battery. Ive charged about a dozen times or more.

When/how often should I completely discharge them?
When/how often should I use the test function?


Thanks,
nwiscan (feeling bad for all the wasted alkalines I have used in my lifetime!)

 

[RBWNY]

Hi & welcome !! :welcome:

I have the same charger. What brand(s) of NiMH's have you been using? Is this the first charger you've owned? I've had mine over a year, and I generally run the cells close to empty (but they say not to do that too frequently) and just do a regular charge. I might've only run the test cycle once or twice. Same goes for "refresh". I did that recently to see how a cheap set of cells I bought from Amazon would respond since from just sitting for a month or two, they lost 80% of their power!! (I guess they're not LSD's!)

Most of my cells are either eneloops or duraloops. Unless someone else has a different opinion, the quality cells should be trusted with a regular "charge". If they were giving you reason to believe they were going bad...losing charge quickly (not holding a charge) or not charging completely, they I'd suggest a test or refresh cycle.

That's MY 2 cents! :wave:

 

[RBWNY]

PS........

I'd probably recommend a refresh if the cells had sat un-used for many, many months.

 

[nwiscan]

Thanks for the responses, look forward to any others.

I have the same charger. What brand(s) of NiMH's have you been using?

Im using the BC-700 with a pack of energizers, duracells and eneloops just to try an assortment.

I have been recharging them only when my radio that is used daily says they are low (1.2 volts or thereabouts). Since that is not depleted thats why I am concerned if I should be completely discharging, or refreshing once a week/month or at some sort of interval. In the said radio, they seem to last about 12 hours and then I swap them out and put the others on the charge for 500.

Thanks, still learning.

 

[SilverFox]

Hello Nwiscan,

Welcome to CPF.

In general you do a complete discharge when you notice the run time getting shorter than you think it should.

On the other hand, if you do a complete discharge once every 3 months or so, you can miss out on the reduced run time.

Tom

 

[45/70]

Hi nwiscan, and welcome to CPF!:thumbsup:

If the cells you are using in your radio all read around 1.20 Volt when removed after the battery low warning comes on, you probably don't need to do anything more than that. Just charge them up again.

Maybe once or twice a year, you might do a deeper discharge to 0.90 volt, using your La Crosse. The fact is though, that if your cells are reading close to 1.20 Volt when removed from your radio, they are pretty much discharged. There is not any significant capacity left in a NiCd, or NiMh cell at this voltage. In fact, unlike NiCd cells, NiMh cells actually prefer not to be discharged lower than 1.20 Volt/cell (no load, or open circuit voltage) on a regular basis, and will actually last longer if not discharged farther routinely. Still as I mentioned though, it wouldn't hurt every once in a while, as fully discharging (to 0.90 volt) helps keep all the chemicals within the cell active. By routinely discharging to 1.20 volts/cell however, your keeping most in the mix.

On another note, if ever you pull the cells and notice that one, or more cells is much lower in voltage than the others, it would pay to keep track of your cells and match them up so that you end up with cells that discharge more evenly.

If one, or more cells were to discharge to the point that the cell's voltage goes into reversal, this will damage that cell, or cells permanently, to some extent. This will not necessarily be detectable when you remove the cells. When this "reverse charging" as it is called occurs, usually, by the time you pull out the cell, the voltage will have recovered to a positive number. Cells used in series applications that read under 1.00 volt when removed from the device, are suspect. This is particularly true if all the other cells are at a significantly higher voltage.

The only solution for this (if you are unable to match up cells that discharge in a similar fashion), is to try to recharge the cells before the low battery warning shows. Then of course, you would need to do a deep discharge (to 0.90 Volt) more often, such as every two to three months, in order to keep the cells vibrant.

Hope this helps,

Dave

 

[nwiscan]

Thank you all for your thoughtful responses, they definetely help!

Im going to monitor my cells for awhile before discharging. Since I am using them in a scanner radio, a shortwave radio, a tac flashlight and a LED lantern.... all of which are daily users, I can keep tabs on run time.

If anyone else has anything to add I would appreciate it.