Sunday, February 7, 2010

Truth in Rechargeable Battery Advertising

Like most of us, I use a number of battery powered devices in daily life. When I started saving spent cells for proper disposal and saw how many of them were being tossed I became concerned. I wanted to cut down on the waste.

In the past I had used Nickle Metal Hydride (NiMH) batteries with a cheap charger. As the charge cycle is not 100% chemically reversible the batteries age. Eventually a battery goes bad and perhaps 1 of 4 batteries is no longer chargeable, but which one ? The charger that I had was really cheap and would only charge in pairs or quadruples. This made trying to find the bad battery(s) in a batch very time consuming.

Time for a new charger. After a bit of investigation I settled on the 'Maha MH-C9000' Charger Analyzer. This device has 4 independent charging circuits so each battery essentially has its own individual charger.
The real usefulness of the device is that has more functions that just charging: Charge, Refresh, Breakin, Discharge.

allows you to set the input current, you can do a high current fast charge or a more battery life friendly slow charge.

does a voltage based charge-discharge-charge cycle in which you get to choose the charge and discharge currents. When finished the total capacity of the battery found during discharge is reported so that you know how much energy the battery will hold at that point in it's life cycle.

does a very slow time based charge discharge charge cycle recommended for new uncharged batteries.

will drain the battery (I haven't had cause to use this yet).

So with the MH-C9000 there is no more guessing about the state of your batteries. Doing periodic Refresh cycles you can see what each battery's capacity is over time and watch its decline (I do a Refresh about every 10 recharges and the slower Breakin about every 30 recharge cycles). When a battery has ceased to be useful, this charger will refuse to charge it and will indicate to you that it has refused.

I decided to measure the capacity of each battery to compare against the capacity stated on the label by the manufacturer. I've done that for a number of new batteries and the results are interesting.
See the graph above (hand drawn, the old fashioned way).

For a given set of new batteries, I averaged the measured capacity and graphed the percentage deviation from the labeled capacity with negative percentage on the Y axis thus the higher the bar the WORSE the battery. I arbitrarily picked -10% as the GOOD/BAD cutoff point. The GOOD green bars are less than 10% below labelled capacity, the BAD red bars exceed that.

Based on this small sample size, one interesting trend is shown:

The 'Name' Brands tended to be truer to advertised claims than the less well known names.

Most notably, the Radio Shack 700 (the green battery on the left in the graph picture) showed an average capacity of 726mAh which is HIGHER than the 700mAh on its label.

The biggest joke was the visually screaming red and black 'CTA 1200' (the red battery on the right in the graph picture) which yielded an average 389mAh, that's a whopping -68% less than what its label says !

Radio Shack is not known for premium quality electronics but what it does have is warranty support and deep pockets (the U.S. is, after all, a place in which if you were to order a Coke but instead are served a Pepsi, the place that mis-served you is seriously liable).

The next place 'truth in advertising' runners up are both 'Imedion' batteries from Maha. As Maha is the manufacturer of the MH-C9000 it's fitting that their batteries have trustworthy labels !

The Good

AAA Radio Shack 700 actual 726 + 3.8 %
AAA Imedion 800 actual 800 0.0 %
AA Imedion 2100 actual 2070 - 1.4 %
AA Kodak 2100 actual 2038 - 3.0 %
AAA Sanyo 1000 actual 962 - 3.8 %
AA Kodak 2500 actual 2332 - 6.7 %

The Bad and Pretty

AA Nexcell 2700 actual 2291 -15 %
AA Accupower 2900 actual 2281 -21 %
AAA Nexcell 1000 actual 623 -38 %
AAA CTA 1200 actual 389 -68 %

1 comment:

thorick said...

Here is a follow up about the conclusion of my multi-year rechargeable battery investigation.
In the olden days it was common to have rechargeable battery packaging claim that the batteries had 'up to 1000x charge cycles' (I think it was 1000).
Note that today, there are no such claims printed on the battery package.

I performed all the maintenance tasks that have been prescribed to get the most life out of NiMH batteries: a full charge discharge cycle every 10 charges and a complete 'reconditioning cycle' (that takes about 36 hours or so) every 30 charges.

What I've found is that despite the care given to the maintenance of the batteries, the vast majority of them were no longer useful by 50 charge discharge cycles. This is regardless of brand or cost of the batteries.

Because of this, I am now free !

No more careful monitoring of battery charge histories and performing maintenance steps.

No, if the majority aren't going to be good for 50 charges, now I'll just recharge when the they need it, and when they've gone to the ion bucket in the sky, they head for the recycling bin.