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Looking for NiMH AA cell recommendations

My GPS uses 2x AA batteries. I’ve been using some long storage life NiMH cells for a good few years now. I’m thinking maybe 6 or 7 years since I bought them. When I first got them, they were excellent. Charge them up and they stay charged ready for use for ages. Now, they seem to have lost the facility to remain charged. Charge them up and a pair will power the GPS continuously as long as before. But they do now seem to have a high self discharge rate. Often within 2 weeks of being charged, removed from the charger and put ready for charging, they have discharged themselves significantly.

I’ll have a play at seeing if they can be rejuvenated somewhat but I need some replacements. So I’m looking for reputable brands of NiMH (1500mAHr or better) that people have used and have had good results from. Also with our friends in China producing astronomical numbers of counterfeit goods now, any recommendation of how to check what I buy are genuine and who to buy from will be gratefully received.

I seem to remember when I got my last GPS, the manual (I know no real man should read those things) recommended Lithium AAs. I got a couple of sets but haven’t actually compared their performance with other types.

Eneloop batteries get consistently high recommendations. The current top of the line is two options with different trade-offs. The battery names might be different in different countries. Both are low self-discharge.

Eneloop 2000: These have ~2000 mAh capacity and are rated for 2100 charging cycles.

Eneloop Pro: These have ~2500 mAh capacity and are rated for 500 charging cycles.

There is some belief that Amazon Basics batteries are the previous generation of Eneloop. Personally, I don’t try to save a lot of money on batteries that go in expensive equipment. I use the previous generation of Eneloop Pro (called “Eneloop XX” at the time) in my KX3. It is about time to replace those. It has been five years.

The Wikipedia page for Eneloop has a useful chart of all the versions of these batteries over time.

wunder

Lithium AA batteries are 1.5 V and 3000 mAh, so more Watt-hours than NiMH, but they are not rechargeable. They weigh half of what NiMH batteries do, so they are a good option for a longer backpacking trip where you won’t be able to recharge batteries.

1.2 V, 2500 mAh: 3.0 Wh
1.5 V, 3000 mAh: 4.5 Wh

wunder

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Mine are rechargeable. Sorry I can’t remember the exact chemistry (I’m away from home at present).

Eneloop batteries are the way to go. I use the 2000 ones as they are cheaper and can be charged significantly more times than the Pro series.

Dave, AE9Q

Let me add my recomendation for Sanyo Eneloop/Panasonic EVolta NiMH batteries. They come pre-charged and hold charge longer than normal NiCADs. They are 1.2v 1950min/2050max mAh cells. The Sanyos are made in Japan, the Panasonics in China.

Ed.

I’ve used Eneloop, Duracell and Energiser, longest lived are the Eneloops still going strong after about 5 years. Bought from “real” shops instead of online in the hope that they’re more likely to be genuine…

I get out so infrequently these days I top up a couple of sets for each outing, haven’t quantified how much charging it takes but between ten and thirty minutes in my plug-in charger does the job on unused cells.

Sound strange but IKEA has low selfdischarge AA and AAA. Internet claims they are basically 100% Eneloop Pro types.

Name: LADDA
https://www.ikea.com/gb/en/search/?k=ladda

Have the AAA for my headlamp in use. So far working flawless.

73 Joe

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I’ve been using the same 2300 mAH Energizer “recharge” AA NiMH cells in my old Garmin Etrex Vista C GPS for many years now. Three pairs of these cells have seen almost 1000 SOTA activations now, plus countless other cycles in headlamps, etc. The Garmin will run longer on 2 of these cells than I can - more than 16 hours, even in the cold. I almost never buy AA batteries for it.

Long ago I learned that many of the inexpensive chargers sold for these cells gradually ruin them. They do a pretty fast charge, but they either don’t stop charging at a high rate soon enough, or they continue with too much current after the charge is done. If the cells get warm in the charger, they probably won’t last as long as mine have.

Despite reading various articles about how to charge NiMH cells correctly, I decided to try using a voltage regulated, current-limited charger. This is a real No-No according to some experts! The secret is not to be in a hurry.

My homebrew charger started as one of the cell-killing chargers I had used previously. Two cells are connected in series and fed from an adjustable linear voltage regulator (LM317T):

  1. The LM317T voltage regulator is set for 3.15V.
  2. A high-quality pot is used for the voltage adjustment.
  3. A current regulator, also based on the LM317T, precedes the voltage regulator.
  4. Current is limited to 300 mA, and a pot control is provided to reduce this to about 250 mA (normally).
  5. A meter and a bulb indicator show the charging current.
  6. The two series-cells being charged also have a 1N5817 Schottky diode in series.
  7. A second pair of cells, also connected with a series 1N5817, can be charged simultaneously. Since the total current is limited, 4 cells need longer 2 cells.
  8. The Schottky diodes prevent interactions between the pairs of cells, and they guard against reverse polarity errors.

Each Schottky diode reduces the 3.15V charging voltage from the regulator to about 2.80-2.85V at the cells. The voltage drop of the Schottky is about 0.3V during most of the charge. However, at very low currents, the voltage drop is less, allowing the charger and the cells to negotiate the voltage near the end of the charge. This allows some reasonable low float current to continue after the charge is essentially complete.

My NiMH cells need to be charged at about 1.42V per cell, when using a simple voltage regulator. This voltage has an inverse relationship to temperature! At 20-25 degrees C, 1.42V per cell is about where you need to be to charge these cells with a regulated voltage and low, limited current. At higher cell temperatures, the end-of-charge float current of a voltage-regulated charger will increase, and this could be a problem if charging these cells in a less-controlled environment than inside my house. However, my charger still works OK, without air conditioning, in the upstairs of our house in summer!

In summer, with the inside temperature at about 30 C, the end-of-charge current rises to as much as 30-40 mA; in winter, with the inside temperature about 20 C, I see the end current about 15 mA.

Note that if you charge at a higher rate, say 1A, the cell temperatures will rise considerably during charge, likely causing the current not to drop sufficiently as the end of charge is approached.

By limiting the charging current to 250 mA, heating of the cells is minimized. This makes the charging procede in a very orderly and predictable way. It also takes longer to charge the cells than most of the commercial chargers.

The charging current starts out at about 250 mA and is limited by the current regulator. Most of the charge is delivered in a few hours, depending on the state of discharge of the cells.

The current decreases gradually as charge progresses, and the cell voltage moves up toward the voltage-regulated input. After the current drops to about 25 mA, I usually remove the cells from the charger. If I forget and leave them on overnight, no harm is done.

An older charger I had delivered about 60 mA to the cells after the end of charge, and this gradually increased the internal resistance of my cells, until they would no longer work effectively outdoors in winter. This might have been due to gradual loss of water from the electrolyte.

One of the best features of my charger is that I can top off my cells anytime, regardless of their state of charge. Ordinary NiMH cells lose energy and voltage on the shelf, but they can be brought up near full power after a relatively short time in the regulated charger. There is no danger of charging too much.

Whatever charger you use, check the post-charge current to make sure it isn’t too high. Also feel the cells to see if they’re getting warm. In my slow charger the cells don’t get warm enough to feel it.

At local stores I see new types of NiMH cells for sale - some of these say they will retain charge for many months. Newer chemistry makes this possible. I have not tried these yet. In any case, they will work best if used with the correct type of charger for their chemistry.

Long charge retention is not very important to me, so I can’t speak to that. My cells still have plenty of charge a few weeks after charging, and they are many years old.

Maximum charge energy and fast charges aren’t what I really need. Long life and reliability are what I’m getting, and I suspect that most people who use NiMH AA’s aren’t getting these kinds of results from the products that they use to charge their cells. They sure buy a lot of one-way AA’s!

Your results may vary…

73

KX0R
George

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I certainly agree that gentle charging is beneficial to cell life. I think one of the reasons my old LiPos are still not swollen and working (albeit with less capacity) is because the charger I used only charges at 200mA max per cell and also seems to stop before cells are fully charged. As I now have a “posh” charger I can see it drop the current as the cells start to approach capacity. I’ll be charging the LiFEPo4 cell at a lowish current for the same reason and as it is programmable, I’ll exchange charging time for cell life. Fast charging I’ll leave to the drone jockeys.

Reading about the charger I have suggests maybe it doesn’t do enough discharging before switching to charge. It certainly charges at quite a high current as the cells are hot, not warm. The cells will still power my GPS for almost the same duration as when they were new but it’s the self-discharge rate that has shot up and in my case, I want cells with a low self-discharge rate. A page on Battery University I think, said the increase in self-discharge in NiMHs is due to the metallic crystals in the electrodes becoming larger and that happens when they are not discharged enough. A possible fix to restore shelf-life is a number of full discharge/charge cycles.

I think it’s worth punting for some Eneloops based on the recommendations, they’re not terribly expensive. I’ll try some discharge/charge exercises on the current cells but if they don’t massively improve it’s not a big issue. They cost £10 for 8 in 2011, I’ve had £10 of use out of them!

I have had very good experience with own-brand cells from 7dayshop.com. In the AA size the nominal capacity is 2900mAh which is obviously not what you get in practice, but they are by a long way the best I have ever had for endurance in my GPS devices.

I have no idea who makes them but I tried them on spec when they were on special offer and they turned out much better than I was expecting.

I ought to say though, that I never rely on them holding charge when idle. I always charge them the day before use and I am more than happy if they last a full day out. These usually do. The Ansmann cells I was using before tended to run out late afternoon.

Martyn M1MAJ

Neither do I. Like you, I always charge 4 AA batteries overnight before the activation.
Never had to use the spare pair in my pocket. One pair of AA batteries in my GARMIN Etrex-10 have always lasted for the whole activating day. I always switch my GPS OFF when I get to the summit and during the SOTA activation, only switching it back ON when I’m going to descend.

The ones I have pretty much always used for my GPS and never let me down are:
GP 2600 series. Made in China. It’s a Product of Gold Peak Group. www.gpbatteries.com
These ones:

73,

Guru

So given all the feedback and similar experience, the real question might be “What charger should I use”. There’s only about a zillion on Amazon that come out of China. I’ve noticed batteries being hot and I have batteries that the unit will no longer charge. I feel like the problem for me is charger ruining the NiMH units.

Does anyone have a recommendation on a decent charger? I prefer one that will charge a lot of them since I use them in photo flash units.

Dear Christian,

First I can support the choice of Eneloop batteries. I use them for all my needs, which is an etrex GPS, flash lights and in the past also a handheld 2m FM radio. For the later I use a new Alinco that comes with a lithium-ion battery now.

When I ran into a problem with my old NiCd/NiMH Charger (batteries weak after short usage) I thought I buy one from the people who should know how to charge batteries. I ordered a combo of charger from eneloop (Panasonic) and a set of eneloop batteries from amazon.

I guess this or a similar item should be available from your local amazon site.

73 Heinz

Hi Heinz,

I also use eneloop batteries, and they get hot in my charger - I suspect that is how it determines when they are charged!

Do your batteries warm up in the eneloop charger? It does seem a good idea :+1:

I’ve just looked at the Turnigy charger that I use for LifePO batteries, and notice that it has a setting for NiMH as well as NiCd and Pb. I’d just have to make a holder with some inter-cell balance connections. That might be another approach…

73
Adrian
G4AZS

I bought Varta rechargers for my gps map66, have a look on screwfixthink they were fiver for 4

They hold charge well

Hi Adrian,

I would not say hot, but the batteries do get warm during charging.

73 Heinz

1 Like

The NiMH charger in the Elecraft KX3 monitors the battery temperature. It won’t charge if the batteries are colder than 0º C or warmer than 40º C.

Eneloop data sheets are available on the web.


wunder

I use one of these for both AA and AAA cells.
https://www.7dayshop.com/products/7dayshop-aa-and-aaa-intelligent-nimh-pro-ds-sc1000-super-fast-battery-charger-multi-mode-lcd-display-ds-127
Key for me is that each charger battery slot is independent and can be monitored. I always keep charging to 200 as this is better for the cell life. As well there are discharge and refresh cycles available at a cell level, although not easy to set up.

This appears to be the same as the Battery Logiic
http://www.batterylogic.co.uk/technoline/technoline-BL700.asp
and as I have both, side to side comparisons have not revealed any differences apart from the price.

I use both eneloop batteries and the 7dayshop versions as mentioned by Martin M1MAJ. However recently Lidl has been selling both AA and AAA batteries that claim the same retention, so I am trying them out.