Tips on charging Ni-MH 'AA' batteries

[RT65CB-SWL]

I am planning to do some basic astro-photography with my compact digital camera. It uses 4x 'AA' batteries.

Does anyone have any tips on charging Ni-MH 'AA' batteries. They say they can recharged 359-500 times. I have one set that has been charged <100 times and they do not last one hour!*

* and that is during daytime hours

[ronin]

3 thoughts come to mind:

Being 1.2volt they may not be out of charge but too low a voltage for the camera after a while, so the camera report the voltage as too low and ceases to operate.

My charger has a switch for Ni-Cd and Ni-MH, make sure it is set to the correct one.

One of the batteries is dead/dying but as it is one of 4 in a series identifing which one is not easy - actually easier to throw all 4 and buy another 4.

I would suspect the first as people see they say AA but don't register the point they are 1.2 volt not 1.5 volt, so are actually only 80% of what most equipment that takes AA's is designed for. Very much like running your car on 3 cylinders and wondering why it doesn't go as fast.

[Psychobilly]

Look for a decent charger that has Delta V and Delta T monitoring of each cell during charging a decent charger will probably switch from fast to maintenance charge as well...

I use Vapextech Cells and Chargers and have used thousands of the cells in products that we made...

http://www.ebay.co.uk/itm/Fast-Smart-Charger-for-1-8-AA-or-AAA-NiMH-batteries-LCD-display-Vapextech-/370587152795?pt=UK_Sound_Vision_Battery_Chargers&hash=item5648b7319b

http://www.ebay.co.uk/itm/AA-8-x-2900-mAh-NiMh-Rechargeable-Batteries-Vapextech-/221258925945?pt=UK_ConsumerElectronics_Batteries_SM&hash=item33840f4779

The voltage point made by Ronin is a valid one...

Peter...

[Carbon Brush]

Good point by Ronin on the 1.2V vs 1.5V.

Many NiCd and NiMH cells are produced in quantity for minimal cost. Reliability is low on the list of priorities. You may just be unlucky. Have you done discharge check on individual checks into a known (small lamp) load? I have found reliability to be poor on 'strange name' cells compared with 'known names'.

Second is capacity. You will find AA cells with as little as 500mAh or up to 2.5Ah quoted capacity. Do not mix them. The manufacturer may (or may not) say under what circumstances this capacity is available. As a general rule a low current for a long time will give the stated capacity. A high current for a short time will give much less. Some perform better than others at high discharge. Then of course temperature is a factor.

Third is charging. A 'clever' charger will monitor cell temperature, actual voltage and rate of change of voltage. Then use this information to fully charge the cells in the minimum time without damage. On completion of charge a much smaller retention current is sometimes applied. A 'bodgers' rapid charger just slams in the current and leaves it you to turn off later, hopefully before harm is done by overheating or overcharging. A rule of thumb for safe charging is to keep current to less than 1/10 of the Ah rating and be patient. In practice the cells can be left on for days without harm.

Finally. Buy a multimeter. This will allow you to measure what is actually going on. Without measuring, you have no quantitative results of cell performance or state. The meter will come in handy for other astro kit, the car and around the house so is money well spent.

Hope something in these ramblings is useful. David.

[JamesF]

I have given up on rechargeable batteries altogether. I think they're particularly poor for astroimaging use when the ambient temperature may well be low.

What I now do is buy Duracell Procell batteries in bulk (by the hundred). They're basically the same as standard "copper-top" Duracells, but something ridiculous like a tenth of the price and it's not like we don't get through AA and AAA batteries reasonably quickly with all the electronic stuff in the house.

James

[L8-Nite]

.......... One of the batteries is dead/dying but as it is one of 4 in a series identifing which one is not easy - actually easier to throw all 4 and buy another 4. ..........

A worth while investment is a battery tester.

[AstroTux]

Second is capacity. You will find AA cells with as little as 500mAh or up to 2.5Ah quoted capacity. Do not mix them. The manufacturer may (or may not) say under what circumstances this capacity is available. As a general rule a low current for a long time will give the stated capacity. A high current for a short time will give much less. Some perform better than others at high discharge. Then of course temperature is a factor.

Something I have noticed is that the higher rated Ni-MH batteries tend to exhibit a higher internal resistance than lower capacity ones. This means that they can produce their rated voltage for quite some time in a circuit that requires little current, but that they tend to drop in voltage as soon as any considerable load is taken out of them. Unfortunately digital cameras, etc. all require quite a high current at power up and can quickly kill the higher capacity NI-MH batteries.

I have given up on rechargeable batteries altogether. I think they're particularly poor for astroimaging use when the ambient temperature may well be low.

Quite.

If you're using AA batteries you could also invest in a load of lithium ones. In bulk they tend to work out at less than £1 each on that well known auction website. The beauty of these is that they have an extended shelf life ( up to 10 years ), push out slightly in excess of 1.5V ( normally about 1.55V ) and can work down to -40° ( C or F, they're both the same ). I now use these exclusively in my camera and GPS when hill-walking in winter as they haven't failed me yet. Ni-MH batteries used to fail every time the temperature got below about -8°C.

Hope this helps,

Alan

[RT65CB-SWL]

I know that Ni-Cd and Ni-MH 'AAs' have 1.2v instead of 1.5v and I never mix them if they are of different capacity when charging or in use.

Thanks for the link Psychobilly. I will proberly purchase one of those chargers. The ones I am using are just 'plug-in & go'.

[Psychobilly]

I use 3 of those chargers they come with a wallwart but can be run on any input voltage between 10-18Vdc which means they work well off car batteries, powertanks etc for charging away from the mains....

I have use Vapextech cells for RC racing, in commercial products (had 1000's of custom packs) and for heavy duty flash use - I sometimes use upto 8 flasguns at a time...

Peter...

Sent from my GT-P7300 using Tapatalk 4

[StuartJPP]

These days I only use Sanyo Eneloop batteries. I have used loads of NiMh cells in the past and they have always suffered one way or another. The main problem I found was self discharge. I had some 2500mAh Energizer batteries that would deliver 2500mAh straight off the charger, however after a week, they halved their capacity and after two weeks they were effectively flat. Now if you are using them day in, day out that is fine, but I don't and need them to work when I am going to use the kit.

Secondly, a decent charger is key to getting the most out of your batteries, or more importantly getting energy into them. Ensure that you get one that can charge individual cells. Most cheap chargers either charge the lot in series or in pairs, which to me is quite pointless. I bought a Maha MH-C104FS charger about 7 years ago and is still going strong. Though if I was to buy one today I'd probably get something like the "Maha MH-C9000 WizardOne Charger-Analyser" or equivalent (see here http://www.batterylo...e-i-charger.asp).

If I had a limited budget I'd get this:

http://www.7dayshop....XN0ZXJzI3A9Mg==

Remember that the claims that batteries can be charged 1000's of times is a bit exaggerated and each time you charge/discharge them a little bit more capacity will be spent. So after a number of cycles you may only be at 80% of the original stated capacity.

As JamesF mentiones, buying a lot of AA batteries in bulk can be just as cost effective depending on the application. Modern compacts are a lot more energy efficient, but I am not 100% sure what their demand is (years ago they were extremely current hungry). However alkaline batteries just cannot compete with high load demands (such as charging a flash) so if you only need them purely for lighter use, then that may be the better option...though personally I hate throwing batteries away.

[JamesF]

As JamesF mentiones, buying a lot of AA batteries in bulk can be just as cost effective depending on the application. Modern compacts are a lot more energy efficient, but I am not 100% sure what their demand is (years ago they were extremely current hungry). However alkaline batteries just cannot compete with high load demands (such as charging a flash) so if you only need them purely for lighter use, then that may be the better option...though personally I hate throwing batteries away.

I do too, to be perfectly honest, but after quite some years in denial I just decided it was far more sensible to have a load of batteries that I would get full use from once than to have a load of rechargeables that often don't work that well and that need regular recharging or you never have any fully charged when you want them. It offends my "eco" sensibilities somewhat, but I'm not yet convinced that using alkaline batteries is the worse environmental option anyhow when you take into account the way that many rechargeable batteries actually get used.

James

[1parsec]

I'd go with StuartJPP recommendation. I also use Eneloops and wouldn't use any other type.

I'm not sure of the cold weather capacity of them though.

I use this charger http://www.batterylogic.co.uk/technoline/technoline-BL700.asp and it does recharge the batteries close to full rated capacity.

Dave

[StuartJPP]

I'm not sure of the cold weather capacity of them though.

Cold weather will affect most batteries, but as mentioned lithium batteries cope the best by far however they can be pretty expensive. There isn't a one size fits all I'm afraid.

That battery charger (BL700) is the one I recommended to my brother, he is well chuffed with it.