UKH

A question about rechargeable batteries - AA & AAA type in particular.

Is it as simple as the mAh rating being relative to how high a charge is held and thus how long they take to run out?

I'm looking to buy some AAA's, would I be better off getting 950 mAh rather than 600 mAh - prices being similar?

Thanks,

Glyn

In principle you are right, higher capacity will last longer, but there are a couple of gotchas to watch out for.

The higher capacity batteries will probably self discharge faster. If you charge them then use them soon then they'll be fine. If you leave them a few months they might be half flat again.

Secondly, batteries bought on the cheap off the internet may just be rubbish and the high capacity just a lie to make you buy them. The more logos saying "long life", "ultra high power", "super digital HD ultra GTi" etc. The worse the battery will probably be!

Eneloop batteries used to be well regarded, their AAA is 750mAHr. Capacities much more than that should be treated with suspicion!

I'd second the reply above.

I used to have some Duracell and Eveready batteries wih 2650mAh and 2500mAh ratings respectively (AA size) and found their performance quite poor.

I swapped them for Eneloop with a 2000mAh and the improvement was really significant.

You also want an "intelligent" charger that charges each battery separately like this

https://www.amazon.co.uk/Youshiko-YC4000-Intelligent-Professional-Standard/...

Standard chargers treat all the batteries as if they were one unit so don't bring each up to peak capacity and have other effects which can even start discharging some batteries within a batch.

Charging on the slowest setting is also best for the batteries where possible.

And a third for eneloops plus a half decent charger. 

Brilliant - thanks

Thanks, useful information. If I charged batteries individually on my existing chargers would that give better results?

Also do NiMH still have any memory like NiCd and lose some capacity if charged before fully discharging (I am under the impression they don't)? Also do recent threads mentioning advantage in not fully charging or fully discharging batteries apply to NiMh?

Apologies about piggy backing on the thread.

I'm not an expert on this but I'd imagine so. When you "block charge" several batteries some will reach capacity before others so they are overcharged.

I did some reading up on this sort of thing a few years ago when I ended up buying the smart charger and eneloops but in all honesty I can't remember enough to answer your questions! Sorry.

BTW, I think the market leader in smart chargers is the Technoline model

https://www.batterylogic.co.uk/technoline-bl700n-battery-charger.asp

No, dumb chargers tend to always charge at a fixed rate, so either a quick charge or slow depending on the model. Optimal performance comes from quick charging and then switching to slow at the right time, judged by monitoring the individual battery.

Re your second question, I suspect there is some kind of 'memory effect' of recharging from mid state of charge but it's nowhere near as bad as it used to be. And these smart chargers offer a refresh option where they can reduce it by a series of deep discharge and recharge cycles and bring back performance, so it's not a one way street to oblivion.

I've had good results with the Uniross AA batteries, after previous recommendations on here, but not tried their AAA. Also Duracell and Energizer AA ones.

My Energizer 850mAh AAA ones seem to have lasted pretty well.

Edit - note that rechargable AA/AAA seem to be universally 1.2 volt, rather than the usual 1.5 volt and don't work so well in some applications. A typical 4xAA pack would be 6v, but with rechargeables will only be 4.8v.

As folk have said, the larger the capacity the longer (in Theory) the battery will last.  I've been using the same AA high capacity Eneloops for years and they've been really reliable, with minimal self discharge over time.  Definitely invest in a smart charger; plenty good models out there, but also think if there are battery types other than AA/AAA you want to use to future proof.

General rule of thumb is that the faster you charge the batter, the greater the decomposition and shorter the life so whilst there are times you want/need a fast charger on the whole a slower overall charge rate is better in the long run - lots of smart chargers will let you choose the charge rate or give you fast/slow presets.

Refreshing function is good too - takes an age to actually do but definitely breathes new life into batteries!

Check the devices you want to use them with - not everything will run off rechargeables; it'd be too easy if AA/AAAs will all the same voltage output!!

Cheers!

Stu