If you’re still buying single-use batteries, one or two at a time (or even several dozen at a time), and throwing them away as each one is depleted, you’re still living way back in the twentieth century.
New developments in rechargeable battery chemistries combined with massively improved ‘intelligent’ battery chargers have made rechargeable batteries much better and more affordable for almost every type of battery using electrical and electronic device.
Our mobile phones, tablets, and some other products use Lithium-ion (Li-ion) batteries, and that’s a different type of battery entirely, but most other products, from remote controls to flashlights to clocks to thermometers and so on, throughout your household, are designed for either standard 1.5V batteries, such as AAA, AA, C or D types, or perhaps standard 9V batteries.
These types of batteries have interchangeable rechargeable batteries of the same shape and size, and similar voltage, and almost without exception, any device that uses standard sized single use batteries can use rechargeable batteries too.
Two Types of Rechargeable Batteries
The original rechargeable batteries were Nickel-Cadmium (Ni-Cd) type, but in the 1990s they were largely superseded by Nickel-Metal Hydride (Ni-MH) type batteries. Both create 1.2 volts, but the Ni-MH batteries store more charge, can be recharged more times, and don’t have as severe a ‘memory effect’ issue that plagues Ni-Cd batteries. The memory effect is what happens if you only half use a battery’s charge, and/or partially recharge it up. After a few such experiences, the battery ‘forgets’ its total charge capacity and loses its unused capacity.
As good as they were, original Ni-MH batteries suffered one big weakness. Their rate of ‘self-discharge’ was very high. A charged battery, just sitting on the shelf and not connected to anything, would lose its power all by itself, with perhaps 10% of the power disappearing in the first day, and the balance over the next three to six months.
But a new technology – low self discharge – has revolutionized that issue and now Ni-MH batteries seem to be the clear winner in almost every application.
The Pluses and Minuses of Ni-Cd and Ni-Mh Technologies
Many people say that the newer Ni-Mh technology has replaced and obsoleted the older Ni-Cd technology. While that’s a reasonably fair description of what has happened, in actuality there are a very few remaining applications where Ni-Cd technology is superior.
Basically, if you have a device that draws a high rate of current, Ni-Cd batteries may be better. That’s why some of the highest tech airplanes still have Ni-Cd rather than Ni-Mh batteries, for example, and it is also why if you have a power drill, it also probably has a Ni-Cd battery.
But for most other medium and low current applications, Ni-Mh is invariably the better choice. These batteries can hold more charge in them and the latest technology Ni-Mh batteries can be recharged more times than is typical for Ni-Cd batteries. What’s not to like about that!
Not All Ni-Mh Batteries are the Same
So which are the ‘best’ Ni-Mh batteries to buy? That’s a key question, but its answer requires appreciating the different factors involved (of course you can skip down to where we answer the question if you wish!).
There are a couple of measures of how ‘good’ a battery is. The first is how much capacity it has – how much charge it can store. The second measure is how many times it can be recharged. Let’s consider both these issues.
Battery capacity is usually measured in mAh – milli Amp hours. A rating of, eg, 2500 mAh means that the battery can deliver current at the rate of 2500 mA (ie 2.5A) for one hour, or at a rate of 1000 mAh for 2.5 hours, or any other combination of amp rate and hours to come to the 2500 result when you multiple current rate by time it is drawn off.
Now there’s a simplification in the above statement. The amount of charge or current a battery can give off depends on the rate at which the current is being taken. A high rate of discharge will give a lesser total current capacity than a lower rate of discharge.
So, what rate of current discharge does a battery manufacturer use when rating their battery? Unfortunately, there is no universal standard, so it is possible that one AA battery, rated at 2300 mAh of capacity, might actually give less ‘real world’ current than a battery from a different manufacturer rated at 2200 mAh of capacity.
The only way you can accurately compare two batteries is to buy a supply of each and then test them in the appliances you wish to use them in and in that real world setting, decide which gives the better life.
In any event, with batteries that can be recharged hundreds and possibly thousands of times, the amount of charge per cycle isn’t of as great an importance as it is for a single-use battery. More capacity is always better than less capacity, but it isn’t the most overriding issue, as is indicated by the next point.
This is a bit like scoring an ‘own goal’. Once you’ve charged up a Ni-Mh battery (or a Ni-Cd for that matter, too), the battery then starts losing its charge, all by itself, even when not connected up to anything. This is called its ‘self discharge’, and some batteries have much faster self discharge rates than others.
On the other hand, self discharge is no big deal if you are using the battery in an application where it will have all its charge drained out of it within a day or two anyway. But if you are, for example, using a Ni-Mh battery to power your wall clock, and are hoping for a year or more of life from the battery, then the self discharge rate will deplete the battery very much more quickly than the clock’s power consumption will, and so becomes an important factor.
To tie it in to the previous point about battery capacity, many Ni-MH batteries get ‘used up’ not by giving out their power to the device they are in, but by their rate of self discharge. The rate of self-discharge is therefore more important than the amount of charge (most of the time).
Unfortunately, you’ll not see any rating on most batteries for what their self discharge rate may be. Some batteries may be labeled as having ‘Low Self Discharge’ or something like that, and probably they are better than batteries that are totally silent on the subject. In addition, the Eneloop batteries made by Sanyo/Panasonic have enormously low self discharge rates, claiming to still have 75% of full power after three years of storage.
You don’t get nothing for nothing, however, and the low self discharge rate is reflected in a reduced battery charge capacity. Whereas modern state of the art Ni-MH batteries in an AA form factor, but with fast self-discharge rates, can store 2500 mAh and up to almost 3000 mAh of charge, the low self discharge rate batteries are more commonly found with capacities of about 1900 mAh.
If you have an application where you’ll use up all the battery’s charge in a day or two, then you don’t care about self-discharge rates, and instead want the largest capacity possible. An example of this might be to power walkie-talkies that you’re using every day during some sort of event.
But if you’ve a battery application where you use the battery only a very little, and normally would expect many months or even years between replacing batteries (for example, in a clock or a stand-by flashlight or a remote control) then the low self-discharge is a better choice.
The third measure of a rechargeable battery is another very fundamental consideration. How many times you can you recharge it?
Can you guess what we’re about to say next? Alas, many manufacturers are silent on this measure too, and others adopt varying standards for determining how many times they say their battery can be recharged. Duracell simply says ‘These Ni-Mh batteries can be charged hundreds of times’ – but does this mean two hundred or nine hundred?
To be fair to the manufacturers, the number of recharge cycles a battery will accept depends on many things such as the type of use it is getting, the temperature it is being used at, and the type of recharging it is being given, too, which is why we point out that your choice of charger is at least as important as your choice of battery (chargers are discussed a bit further on in this article).
Furthermore, a battery doesn’t just go stone cold dead after a certain number of recharges. All that happens is there is a steady degradation in the amount of storage capacity the battery has. At what point has this become unacceptably short? With rechargeable batteries freely available and inexpensive, many people consider that when the batteries have lost a third to a half their capacity, it is time to replace them. But if you are willing to accept less storage per charge, there’s no reason not to keep reusing and reusing them well beyond their rated life.
There’s no easy way to compare manufacturer claims for recharge cycles (do you really want to discharge and charge a battery potentially 1,000 times to see what happens?).
It seems though that the Eneloop batteries credibly claim to be capable of an unusually large number of recharge cycles – current products claim 1500 recharge cycles. We don’t know exactly how they make that claim, and although we wrote and asked them, they have not answered to explain.
The Best Batteries
Most of the time, the best batteries to buy are the Eneloop
Note that the Eneloop batteries these days come in two types – the long life ones with about 1900 mAh of capacity, and a shorter life but higher capacity one with about 2400 mAh of capacity and a slightly faster (but still outstanding) self discharge rate. The higher capacity batteries also accept fewer recharges.
The longest life Eneloop batteries cost slightly more than $2 each. You can recharge them 1500 times – maybe even more if you’re willing to accept the reduced storage capacity each time – so you are getting about six battery charges per cent of battery cost.
Or, to put it another way, an Eneloop battery costs four to five times as much as a single use alkaline battery. But you can use it 1500 times rather than once. The Eneloop battery is therefore about 300 times better value than the regular alkaline battery.
There’s one more vital component to the ‘best’ battery. It is only as good as its charger. And so…..
Recharging Your Batteries
The value you get from your rechargeable batteries is directly linked to the quality of your recharger.
You probably already know there’s a complex science associated with charging and maintaining lead acid type batteries (golf cart and car batteries), and that you can harm those batteries by incorrect charging, or overcharging, or by allowing them to discharge down to zero. So it should come as no surprise to learn that you can definitely harm your rechargeable batteries if you don’t optimize your charging procedures.
You can harm a battery by charging it too quickly, and you can harm a battery by overcharging it. Cheap chargers and fast chargers threaten to do either or possibly even both of these things to your valuable batteries. Do not economize on your charger(s).
A good charger will recondition and somewhat restore a battery, helping it to recover from neglect or severe depletion of charge, and will get the maximum possible life out of it – more recharge cycles and a slower reduction in capacity per recharge. A good charger can also give you real-time reporting on the capacity of the battery, and help you to understand which batteries are nearing the end of their lives and which are still in good shape. This is not just interesting but essential, because it means you can match up batteries of similar remaining capacity for your devices. It is not a good idea to have, eg, a 2500 mAh battery paired with a 1500 mAh battery – that means you’re only using 1500 of the 2500 mAh capacity of the better battery, or alternatively, you’re harming the lower capacity battery by over-discharging it. Better to have two batteries of each about 1500 mAh.
For example, I had a set of four batteries fail in a radio. Normally I’d need to throw them away and replace them with four new ones. But using an intelligent charger, I was able to test the four batteries and discovered three were still in good condition and one had failed. The charger saved me from throwing away three perfectly good batteries along with the one failed battery.
Good chargers have multiple sensors and complex electronic control circuitry to monitor the batteries you place in them. There is one clear ‘best of breed’ charger that we recommend – the La Crosse Technology Alpha Power Battery Charger, BC-1000
You can get generic chargers for $10 – $20, but these lack most or all of the features of these intelligent chargers, and risk harming your batteries and reducing the number of recharges they will accept. It is massively false economy to couple your investment in rechargeable batteries with an under-featured unintelligent charger.
If you wish to spend less than $60 on a charger, there are options almost as good as the BC-1000. There is a slightly less featured La Crosse charger with a lower maximum charge rate, the La Crosse BC-700
On the other hand, the La Crosse BC-1000 unit comes complete with eight rechargeable batteries and four each C and D cell sleeves, which compensates for some of the dollar difference between it and the two lesser priced alternatives. It also has a convenient carry bag to keep everything in – something I find invaluable because it saves me from losing any of the parts (such as the power transformer that plugs into the wall); I can keep everything stored in the one bag.
The ability to use the La Crosse BC-1000 unit more flexibly so as to possibly be doing different things to each of the four batteries in it at any given time can be useful. Its greater charge rate can also be helpful if you’re in a hurry to recharge some batteries, but with the low self-discharge rate of the Eneloop batteries, you can realistically store your rechargeable batteries in a fully charged state and expect them to still be close to fully charged, even a year or more later.
These days rechargeable batteries no longer suffer from any of the limitations that in the past made us reluctant to use them.
The latest Eneloop style batteries have long shelf-life while fully charged, can be recharged 1500 times, and only cost four or five times what the cheapest AA alkaline battery would cost, making for an extraordinarily huge payback on their trivial up-front cost.
When coupled with an intelligent charger, Eneloop batteries should become the only type of battery you have in your house.