Best AA rechargables.

[Dave Plowman (News)]

Have a much loved ancient Ryobi hobby drill which takes 4 AA cells. Obviously, they've been replaced over the years. Probably originally Ni-Cads.

Checking the current the device can take at near stall speed with a bench top power supply, shows it can take up to about 2.5 amps at 4.8v.

Checking all the AA cells (NiMH) I have lying around by going across them with a DVM set to 10 amps shows the most the best can deliver is under 2 amps - and the worst very much less at about 1/2 amp.

Any make to go for as replacements? Capacity isn't that important as it only gets used occasionally.

I'd love to find another tool that is so convenient as this one for the sort of things I use it for. Most of the current cordless ones are a lot bigger and less wieldy.

[eastender]

Which? gives these three as best buys:

Duracell Recharge Ultra (2,500 mAh - these came in in Sept 2015) - rating 79% Panasonic Eneloop Pro - 78% Duracell Recharge Ultra (2,400 mAh) - 77%

These have the best high drain lifetime and also a good charge retention, although thety ate not the best in time to charge.

E.

[Bob Minchin]

I'd agree that the "pre-charged" type are possibly the best to go for as not only do they tend come from the big brands but also have very much lower self discharge which is essential for a less regularly used power tool. Ordinary NiMh cell will almost certainly be flat/low state of charge simply down to self discharge, each time you come to use the tool

[Capitol]

I buy Xtreme rechargables, from Amazon.

[The Natural Philosopher]

And unlike NiCd, they are permanently damaged by going flat.

[Tough Guy no. 1265]

There's a reason they came with Ni-Cads. They have three times the discharge rate that Ni-mh ones do, so your drill won't stall. Get some more and charge the thing every month regardless - sorted.

[Tim Watts]

I like Panasonic Eneloop Pros

[pamela]

NiCads deliver greater current than NiMHs but, even though you say you don't mind, their poorer capacity (and faster self-discharge) would put me off them when compared to Eneloops.

Perhaps wear and tear has increased the internal resistance of your Eneloops to make the full circuit resistance when measuring with your DVM too great to genuinely draw a 10 amp current resulting in those 2 amp readings.

The following (slightly dated) test shows AA Eneloops continuously delivering 10 amps for over an hour. Other brands too.

If it was me, I would try some new Eneloops.

[Martin Brown]

Using NiCads will get you the higher stall current. Otherwise try NiMH with the low self discharge feature or be prepared to always be cursing your drill for being flat and the batteries to a short painful life.

I find the red ones sold precharged in Aldi/Lidl from time to time about as good as any. Can't remember which one does them.

[Brian-Gaff]

I don't know ho really makes them but I've been impressed by the ones branded as Maplin recently.

Half the issue I find with high current devices are the battery holders which corode at rivets and on the surfaces where the battery connects after a few years. Brian

[Brian-Gaff]

Yes, but most are now the new ones with low self discharge. the whole snag with rechargeable when used in series is the fact that if one cell discharges to a low voltage it is reverse charged by the others through the load, and as has been said, no rechargeable likes this for very long. Brian

[pamela]

Agreed. NiCads perform better but:

Unreliable manufacture meant many of my AA NiCads packed up early. Inconvenient due to low capacity and self discharge compared to NiMH. Possible memory effect. Harder to find and higher prices.

I aim for an easy life. If Eneloops drive the drill then use them. I'm not sure Aldi/Lidl cells would perform as well as Eneloops although I wonder if they may be re-badged Ansmann which is what some of their chargers are.

[Dave Plowman (News)]

If only. ;-)

[pamela]

Got to admit 10 amps seems like a stonkingly high current from a single cell but that's what the test report is saying. I didn't read all the details but I saw the charts.

[Andy Burns]

Look closely, it's just a _very_ small decimal point in 1.0A

[pamela]

The legend to the charts clearly shows "10.0 Amp Test" and the posts also discuss 10 amps.

I suppose 10 amps is theoretically posible because the internal resistance of an NiMH cell is about 0.10 to 0.14 ohms. Maybe if the tester is getting 10 amps then he could be almost shorting the cell.

Maybe it's not all so crazy because a NiMH can probably deliver 3C if pushed, so it might deliver something above 5 amps.

Hey, enough theory. I would just buy the Eneloops and see if they work!

When I test current drain from an NimH (with a much more modest current) the current rises slightly but noticeably from the initial value. I have no idea why. Maybe I have a crap meter.

[Andy Burns]

Oh sorry, I hadn't scrolled down half a mile to that section!

It seems to last under 10 minutes, rather than over an hour as originally stated

[cl]

Ay? 10 AmpHour AA Cells, I don't think so!

Did you mean 1.0 amps for over an hour?

[Dave Plowman (News)]

10 amps for one hour would suggest a capacity of approaching 10 amp hours.

AAs are more like 2.5 amp hours. (2500 mA.hr) But probably could manage nothing like 2.5 amps for an hour.

[Martin Brown]

There is something wrong there. At 10A discharge rate AAs start getting awfully warm by about 30s and could explode after less than 5 minutes.

Most AA's can't get anywhere near that current. Alkalines will though.

Even at 1A continuous current the nominal 2.5Ah capacity or so is already 10% less than you would get at a low current discharge rate.