Hi, I’ve got some Duracell,stay charged nimh 1.2v 800mAh batteries.
I’m wondering what is the best or recommend charge rate for them, 200/300/500/700 mAh ?
I’ve had a search but I didn’t really find a satisfactory answer, or more to the point a answer from a source I could trust.
So thought I’d ask on here to be sure of getting the correct info I need.
Any help much appreciated,thanks
0.5 to 1C is usually a safe bet.
I charge my AAA Eneloops at 300 mAh’s.
200-300mAh, you can charge at 1C but it will reduce battery life and often cause overheating which also reduces battery life
In general you want to stay at 0.25C or less for NiMH battery charging
1C is perfectly fine for NIMH batteries, at least the ones I use.
Maybe it’s different for RC batteries than AA or AAA batteries?
They are made to run several hundred amps, so that could be the reason.
According to many sources you want to stay well below 1C to maximize life. Mind you if you charge once a month “only” getting 500 cycles vs 2100 may not matter to you.
Depends partly on the charger and how it detects a fully charged cell.
It’s worth reading up on the details; any briefly stated definite opinion has to include assumptions about things that may be different for you.
Lower voltage over more time is generally better, but a dumb charger can fail to detect when a cell is full and eventually cook it even when charging slowly.
This may help: NiMH battery technology, how to charge Nickel Metal Hydride Batteries tutorial for design engineers, as well as NiMH chargers.
thats pretty outdated
Cool thanks for all your fast replies 
One more question if I may, now I’m more used to using li-ion ’s
But I use these aaa batteries in my key ring torches so probably charge then once a week, does it hurt them to run then flat and does it reduce the amount of use cycles I would get out of them, and is there any benefits to using the nimh refresher charge cycle setting on the opus 3100 occasionally.
Thanks
Here’s another useful page
For my AAA I always prefer 300 or 500 mA (depend of urgency for charge).
For AA normally I charge at 700mA
> outdated
Yes, but a lot of the NiMH chargers out there are also outdated.
Avoid the old or cheap dumb chargers and those cautions aren’t needed.
in the old days they used to say completely discharge to reduce memory effect, in NiMH there’s no need, but i doubt your losing a lot by draining them, though try to charge before completely empty, even at 20% would probably be easier on the batteries.
The refresher cycle is using up charge cycles, no harm but if your exercising them and not noticing problems theres probably no real need. I used to sometimes capacity test my NiMHs, though with eneloops these days there is no real need to
indeed, i recommend only smart charging, the Lacrosse BC700 and BQCC17 eneloop chargers are highly recommended. Some of the lithium chargers that also do NiMH are apparently good, though i would check HKJs review of it before trusting it
Agreed, that is how I do my Eneloops. I usually do about .75C unless I am in a hurry.
Charging below 0,25C can make some chargers not to detect the dV cutoff, best is to stay at about 0.5C if it has to be fast at most 1C for longlife
With fancooled fast chargers you can push it to 2C but you reduce the battery life a lot
Never had a problem at 500mA, and the eneloop charger is 350mA iirc, seems to also have no problem.
At 200mA (or 1/10C) on AA you might miss the termination
Just looked up duracell aaa ni-mh specs
aaa 850 mAh
slow-fast charge is .5C-1C
so 300 should be fine and up
Good chargers will do 1/10 on new cells
you may not have the best charger and its better to have some more current to get 100% termination
There are multiple chargers tested from HKJ good for lithium but problems with NiMh termination, even quality brand ones that are not cheap
Hi dw911,
you mentioned OPUS BT-C31000. If this is the charger you use then all currents you mentioned in your original post (200/300/500/700 mA) are fine for charging AAA Ni-MH batteries.
OPUS BT-C3100 seems to use CC-CV charging with 0dV termination, that means it will lower the charge current as the battery gets full (prevents overheating) and will always terminate correctly even with small currents. I like OPUS BT-C3100’s charge algorithm a lot.
People say the lower the charge current the higher the cycle count. I tested a similar battery - DURACELL ULTRA 850 - charging and discharging at 500mA and got 142 cycles out of it - DURACELL ULTRA 850 · AA Cycler. If you are going to charge your batteries once a week at 500mA they will last you 3 years…
BTW, usually I charge AA at 1000mA and AAA at 500mA.
Cheers,
AA Cycler