Discharge Rate for Cycling AA / AAA Batteries

[Witterings]

What discharge rate should I be using to cycle AA / AAA batteries?

 

[roostre]

The "AA Cycler" website ( http://aacycler.com/ ) compares various brands of NiMH batteries.

The charge and discharge rates they use for testing are listed at http://aacycler.com/about/how/ :

For AA sized NiMH cells, they use a 1000 mA charge rate and a 500 mA discharge rate.

For AAA sized NiMH cells, they use a 400 mA charge rate and a 200 mA discharge rate.

 

[Witterings]

The "AA Cycler" website ( http://aacycler.com/ ) compares various brands of NiMH batteries.

The charge and discharge rates they use for testing are listed at http://aacycler.com/about/how/ :

For AA sized NiMH cells, they use a 1000 mA charge rate and a 500 mA discharge rate.

For AAA sized NiMH cells, they use a 400 mA charge rate and a 200 mA discharge rate.

Brilliant thank you for that ... much appreciated

 

[Witterings]

Afterthought of a question ... how come the discharge rate should be approx 1/2 the charge rate ... I flew RC things for a few years using Lipo batteries that drained a battery in 10 mins yet recharged at 1amp for a 2000mah battery ... i.e 2 hrs.

Can NiMH not handle the same discharge rate?

 

[roostre]

I assumed that you were cycling NiMH batteries to refresh them, but maybe I misunderstood your original question, so here is some clarifying information.

Typically the "mA charge rate" for AA and AAA NiMH batteries is recommended to be at least "0.3 times the mAh capacity of the cell" (to help ensure the charge terminates correctly) and below "1.0 times the mAh capacity of the cell" (to avoid damaging the battery).

The maximum "discharge rate" for a NiMH battery is much greater than the maximum recommended "charge rate", but lower "discharge rates" provide more consistent results when using "Analyzing Chargers" for comparing and refreshing battery capacities.

In this case "AA Cycler" used "Opus BT-C2000" chargers (and clones of the BT-C2000) with their built-in "Discharge-Refresh Mode". This mode cycles the battery three times and only allows you to choose certain "discharge rates" and then the charger automatically uses a "charge rate" that is twice the "discharge rate". There is also a built-in "Charge-Test Mode" that functions differently (you select the charge rate) and only cycles the battery once.

When "AA Cycler" previously used "SkyRC MC3000" chargers (which allow both the charge and discharge rate to be selected), they used a "charge rate" exactly equal to the "discharge rate" and they selected 1500 mA for AA and 500 mA for AAA cells.

If you know your typical "discharge rate" and your charger can select a "discharge rate" independently from the "charge rate", then I would use that for comparing the batteries that you use. I mostly use NiMH batteries in devices with low-discharge rates, so the built-in Opus settings work for me and also allow me to compare my results with those from "AA Cycler".

I charge many NiMH batteries and use three "Opus BT-C2400" chargers (basically identical to the Opus BT-C2000). The "Opus BT-C2400" (and Opus BT-C2000) will not charge Li-Ion batteries, so I use "Opus BT-C3400" chargers for those. While the "Opus BT-C3400" does charge NiMH batteries adequately, I prefer to use the "Opus BT-C2400" instead of the "Opus BT-C3400" for NiMH batteries because (in my opinion based on my experiences) it terminates the charge on NiMH batteries more accurately (not under-charged or over-charged).

 

[yellow]

Interesting.
I thought - till now - that would be way too low.
Most of my chargers would make the cells - possibly - only hot, but not end charging, when under 1 C
(with just a few cells, but...)

I would opt for:
1 * C (1 * capacity) when nice to the cells,
1.5-2 * C, when quick
= 2 A for AA cells

 

[roostre]

The manuals for most "Analyzing Chargers" provide helpful recommendations.

Check out the "General Battery Education" section in the "Powerex MH-C9000PRO" analyzing charger manual (which only charges NiMH batteries):
https://powerex.helpdocs.com/manuals/user-manual-mh-c9000pro-professional-charger-analyzer

And for NiMH and many other battery chemistries; check out the "Battery Knowledge" and "Battery Voltages" sections of the "SkyRC MC3000" analyzing charger manual:
https://www.skyrc.com/download/MC3000_Instruction_Manual_V1.17.pdf

 

[Witterings]

I assumed that you were cycling NiMH batteries to refresh them, but maybe I misunderstood your original question, so here is some clarifying information.

Typically the "mA charge rate" for AA and AAA NiMH batteries is recommended to be at least "0.3 times the mAh capacity of the cell" (to help ensure the charge terminates correctly) and below "1.0 times the mAh capacity of the cell" (to avoid damaging the battery).

The maximum "discharge rate" for a NiMH battery is much greater than the maximum recommended "charge rate", but lower "discharge rates" provide more consistent results when using "Analyzing Chargers" for comparing and refreshing battery capacities.

In this case "AA Cycler" used "Opus BT-C2000" chargers (and clones of the BT-C2000) with their built-in "Discharge-Refresh Mode". This mode cycles the battery three times and only allows you to choose certain "discharge rates" and then the charger automatically uses a "charge rate" that is twice the "discharge rate". There is also a built-in "Charge-Test Mode" that functions differently (you select the charge rate) and only cycles the battery once.

When "AA Cycler" previously used "SkyRC MC3000" chargers (which allow both the charge and discharge rate to be selected), they used a "charge rate" exactly equal to the "discharge rate" and they selected 1500 mA for AA and 500 mA for AAA cells.

If you know your typical "discharge rate" and your charger can select a "discharge rate" independently from the "charge rate", then I would use that for comparing the batteries that you use. I mostly use NiMH batteries in devices with low-discharge rates, so the built-in Opus settings work for me and also allow me to compare my results with those from "AA Cycler".

I charge many NiMH batteries and use three "Opus BT-C2400" chargers (basically identical to the Opus BT-C2000). The "Opus BT-C2400" (and Opus BT-C2000) will not charge Li-Ion batteries, so I use "Opus BT-C3400" chargers for those. While the "Opus BT-C3400" does charge NiMH batteries adequately, I prefer to use the "Opus BT-C2400" instead of the "Opus BT-C3400" for NiMH batteries because (in my opinion based on my experiences) it terminates the charge on NiMH batteries more accurately (not under-charged or over-charged).

Sorry my comment wasn't totally clear ..... I was only using it as a comparison to express was I surprised the discharge rate was so low.

I'm going through a number of batteries that have been lying around for ages and cycling the AA / AAA's to see if they're totally dead or and need replacing or if they can be bought back to life ..... I'm also going to capacity / IR test a few 14500 / 18650's for the same reason just to see what their health is and replace where necessary.

Cheers fro everyone's help, is much appreciated

 

[Witterings]

havinmg read through the links and tried my charger for cycling I think I'm going to be best off using manual settings ... what should I put as the cutoff voltage on discharge fo AA / AAA ..... I'm guessing Lithium should be 3.2v

 

[roostre]

I only cycle (charge then discharge to test capacity and then a final charge) Li-ion batteries once when I wish to test their capacity (I do not try to "refresh" them with multiple cycling). It is only for NiMH batteries that I occasionally cycle multiple times (up to three and then a final charge) when I wish to "refresh" them (which can sometimes increase their capacity).

Information concerning the "Li-ion discharge cutoff voltage" (which is not user adjustable) for the "Opus BT-C3100" (similar to the Opus BT-C3400) is contained in this thread (Post #5 of the thread includes a recap of what an Opus Distributor told a forum member about this):

Opus bt-c3100 v2.2 discharge cutoff for 18650's

Hello all, I just picked up my first battery charger, an Opus bt-c3100 v2.2. I didn't realize there was a newer bt-c3400 v3.1 available. I have some protected Orbtronic 3400mah 18650's which protect it from discharging below 2.5 volts. I see that the 3100 v2.2 discharges the batteries down to...

www.candlepowerforums.com

Also, in Post #18; a forum member suggests the "NiMH discharge cutoff voltage" is "0.9v (per user manual specs)".

 

[ChrisGarrett]

For AAs, I use 1000mA, since I can't go any higher. For AAAs, I'll do 500mA.

Chris