Battery chargers

[tinpanalley]

So sick of the crappy battery chargers I've had over time. I'm going to stick with eneloops, but I'd like an actual charger that gives me data, remaining charge, time to recharge, etc.. One I'm looking at charges at 200, 500, and 700mA so I'm wondering if there's math that clearly determines what the ideal charging rate is for 2000mAh rechargeable AA and AAA batteries.

 

[Muse]

So sick of the crappy battery chargers I've had over time. I'm going to stick with eneloops, but I'd like an actual charger that gives me data, remaining charge, time to recharge, etc.. One I'm looking at charges at 200, 500, and 700mA so I'm wondering if there's math that clearly determines what the ideal charging rate is for 2000mAh rechargeable AA and AAA batteries.

I'm happy enough with my La Crosse BC-700 battery charger. I use it pretty much exclusively with Eneloop AA and AAA batteries these days. For AAAs I stick with 200ma, although I saw a post recently by a guy who said he does fine using 500ma with his. For AAs I boost it to 500ma. If a battery seems to be crapping out prematurely I can use the restore setting, which will tell me the capacity of the battery eventually. IIRC, if you discharge a battery first, it will tell you the capacity of the battery when it's done charging. However, I don't do that anymore because NiMH batteries are worn in proportion to the totality of the recharge cycles, so doing that test for capacity does cost you. IOW, a complete discharge and complete recharge has the same effect on the ultimate longevity of the battery as two 1/2 way discharges which are followed by recharges.

Time to recharge is something I don't really care about. The La Crosse charger tells you when you place the battery in its chamber what the voltage is initially, and that gives me a ballpark idea of the state of charge and the amount of time it will take to charge it. I charge anywhere from 1 to 4 cells at a time. I also have a La Crosse BC-900 battery charger which was more expensive but I prefer the La Crosse BC-700 battery charger because it is far less apt to give a ".null." rating for an inserted battery if it's severely discharged. In the event that happens I place a cell in one of my other chargers for a few seconds to get a little juice in the cell.

My Eneloops have been so reliable and consistent that I don't bother keeping track of their capacities. If I think there's something wrong, I'll look into it, but it almost never happens. I have been buying them since 2009 and have 40 Eneloop AAAs and 28 AAs.

 

[mindless1]

A lot of people like the Opus BT-C3100 due to its ability to charge more than just NiMH, charge larger cells, and charge them faster. Main down side is the tiny fan has a short lifespan and may need replaced periodically or the case modified to put a better (larger) fan on, but If you just want to charge 4 x AA at 700mA then it won't even need the fan working - maybe for discharge cycling 4 cells, I am unsure about the temperature doing that w/o a fan.

https://www.amazon.com/gp/product/B01852TBOU

There's not a precise mathematical formula for what the cells should be charged at, but for NiMH you want one with (at least) Delta -V charge termination which becomes unreliable if the charge rate is below around C/4, which for the 2000mAh AA would be 500mA. Some people used to say it was even higher than that, but chargers have gotten better over time as long as you don't buy the cheapest junk.

 

[tinpanalley]

There's not a precise mathematical formula for what the cells should be charged at, but for NiMH you want one with (at least) Delta -V charge termination which becomes unreliable if the charge rate is below around C/4, which for the 2000mAh AA would be 500mA. Some people used to say it was even higher than that, but chargers have gotten better over time as long as you don't buy the cheapest junk.

Would you say this La Crosse BC-700 is comparable?

 

[mindless1]

For AA NiMH at 700mA yes BC-700 is a fine choice, for the other attributes I mentioned, no.

Another popular budget choice that can do larger cells and 4.2V Li-Ion is the LittoKala Lii-500 which can sometimes be found on sale for $20 delivered direct from China on gearbest.com or banggood.com, but isn't on sale at the moment and being in China, 3 week S/H wait is typical. Hmm, apparently AT forums doesn't like the merchant that is *** but you can web search Lii-500 charger to find sellers.

There are reviews of a lot of chargers on this site:
http://www.lygte-info.dk/info/indexBatteriesAndChargers UK.html

You can also get a lot of user feedback and less comprehensive mini-reivews on the flashlight enthusiast oriented forums like http://www.candlepowerforums.com/vb/forumdisplay.php?9-Flashlight-Electronics-Batteries-Included and http://budgetlightforum.com/forum/batteries/chargers/reviews

 

[tinpanalley]

For AA NiMH at 700mA yes BC-700 is a fine choice, for the other attributes I mentioned, no.

To be honest, all I'm gonna want is to charge AAA and AA eneloop batteries but to be able to get a reading of their remaining charge, how much longer until a full recharge, and to be using a device that fills them and empties them properly.

 

[cardiac]

I absolutely love my LaCrosse BC-700... Performs flawlessly, and gives good feedback.

 

[tinpanalley]

Just got my BC-700. Doing a "test". Just curious if anyone can help. It says you leave it to go through the process until the mAh and "full" flash back and forth. I'm doing 2 AA at 700. It's been going for about 6 hours. Shouldn't I have seen the "full" by now?

 

[tinpanalley]

Nevermind.. I just figured out what caused the "full" to not appear: impatience.

Perhaps someone could help me out with something else. I'm not sure what I should be gauging results by. It's not written anywhere in the instructions and I think it's because it's something everyone already knows. What is the voltage from full to discharged of eneloop AAA and AA batteries? They both came in at 1946 mAh so that's pretty obvious to understand. Elapsed time was how long that took to test. I was hoping for a realtime measure of percentage until charged fully though, as it went along.

 

[bryanl]

NiMH and NiCads are considered fully discharged at 1.1V per cell. Voltage at full charge should be 1.25V but in practice can be slightly higher, especially immediately after being charged (surface charge). I believe ideal charge rate varies from C/10 up to C, and above C/10 the current must be reduced or completely shut off at full charge, measured by temperature difference, rate of temperature rise, or rate of voltage rise or fall.

 

[tinpanalley]

Sorry, can you briefly explain what C/10 means? If not I'll go look it up. Just want to learn.

 

[shortylickens]

I have a cheap 10-unit charger and it sucks. This thread has been good for me.

 

[mindless1]

NiMH and NiCads are considered fully discharged at 1.1V per cell. Voltage at full charge should be 1.25V but in practice can be slightly higher, especially immediately after being charged (surface charge). I believe ideal charge rate varies from C/10 up to C, and above C/10 the current must be reduced or completely shut off at full charge, measured by temperature difference, rate of temperature rise, or rate of voltage rise or fall.

This could be considered subjective. I consider my cells fully discharged at 1.0V, or 0.9V if I'm pushing it, in a design with a boost regulator. Voltage at full charge, hot off a charger I usually see a little over 1.40V, then settles down to high 1.3(n)V within a day later. A cell that the charger terminates at 1.25V, I'd consider defective if new or short lived if old.