Monday, February 01, 2010

Battery Technology

I do a bit of work in various fields that rely on batteries to run equipment - laptops, servers, desktops, cameras, microphones, IFB, in ear monitors, remote controls, clocks, smoke alarms, building alarms, emergency exit lights, hearing aids and a great deal more.  Because of this, developments in battery technology are somewhat important to me.  So, why not share?  :)

Now, we're talking about two main types of batteries here - the batteries that work when you buy them (primary batteries) and those that don't work when you buy them (broken batt...  oops, secondary batteries) as you need to charge them before using them.

Well, let's forget the Zinc-carbon dry cell as it is crap at pretty much anything - it does run at 1.5V, but it has a low output, low life, limited usefulness.  We'll also completely diss Zinc Chloride (aka Heavy Duty) batteries as they are only very slightly less crap than Zinc-carbon batteries.

That leaves us with the commonly used 1.5V Alkaline (Zinc-Manganese Dioxide) and Lithium (really, Lithium-Manganese Dioxide (mainly) at 3.0V or Lithium Iron Disulfide at 1.5V) primary batteries and various secondary, or rechargeable batteries.  I'll mention both Zinc-air (used mainly for hearing aids) and Silver Oxide batteries here to complete the picture, but will summarily ignore them from this point forward.

As for secondary batteries, I'll immediately ignore Lead Acid batteries (2.1V/cell) as I'm really thinking more of portable batteries in this post.  And I don't mean portable if you wrap a car around it!  :)

Now, NiCads, or NiCd if you spell it properly, are the most inexpensive, most common of secondary batteries.  They are fine for things such as remote control cars, but are crap for radio microphones, IFBs, IEMs and many other things such as smoke alarms and remote controls - mostly because of their 1.2V cells.  The Cadmium in these is a significant environmental hazard and these batteries are being phased out in a number of countries because of this.  They also suffer a "memory effect" where if they are not fully discharged before being recharged, they will o0nly discharge that far before thinking they are empty - this can be addressed sometimes with the use of deep cell recycling/rejuvenation, but there are better battery technologies around.

Like NiMH - Nickel Metal Hydride.  These have the same issue of being a 1.2V cell, making them still not ideal for devices designed for 1.5V cells, such as many radio mics, IFBs and IEMs, however they have the ability to withstand higher discharge rates than Alkaline batteries.  The original NiMH batteries have a crap shelf life - use immediately after charging as they lose 10% of their original charge after 2-3 weeks and about 35% after a year.  Newer "low self-discharge" NiMH batteries lose only about 5% after 2-3 weeks and 15% after a year - they can therefore be quite usable off the shelf most of the time.

Lithium Ion secondary cells have been around for a while now, however they are ~3.6V/cell, making them not so usable in AA/AAA cells, but great as laptop batteries.  They are lighter than pretty much any equivalent secondary battery, however they suffer poor cycle life - each recharge causes them to lose a bit of life expectancy.  They also don't handle high charge rates nor discharge rates well at all.  They are not very good with heat and can explode if overheated or overcharged.  Lithium-polymer cells (Lithium-ion polymer, to be correct) are a variation on this theme which offers a higher energy/weight ratio and a more physically robust design at the expense of needing to be quite carefully recharged.

Then there's the new (well, patented in 1901) Nickel-Zinc batteries at 1.6V/cell that are also looking promising.  They are currently commonly available as AA or AAA cells, however with low environmental impact, high cell voltage (usable in devices that can't run on the 1.2V cells of NiCD or NiMH batteries), fast recharge times, mAh ratings similar to Alkaline batteries, costs approaching those of Alkaline batteries, around 1000 recharges, however with very little real information on self-discharge rates.

So, it looks like for regular 1.2V secondary cells in devices that can handle them, the newer LSD-NiMH batteries, even though they will take fewer recharges (compared to normal NiMH cells) are the way to go, and NiZn in devices that don't work well on 1.2V secondary cells.  I'd really like to see some comparisons on discharge curves of the NiZn vs Alkaline batteries.  I'd like to see NiZn batteries and chargers available in Australia, too!

I could spend a boatload of time Googling everything and anything related to thes ebattery technologies, looking for discharge rates and lifetime plots and such, but I'm very unlikely to find any real comparative figures across different technologies.  I know that the Sanyo Eneloop site has some decent information comparing NiMH and their LSD NiMH Enerloop batteries, and Stefan Vorkoetter has done some more research on these and a few other LSD NiMH batteries.

Out of interest, you *can* recharge some Alkaline cells with varying degrees of success.  You *cannot* do this in a regular NiCd, NiMH, Li-ion nor NiZn charger.  Depending on how discharged they become, you can charge them up to a few hundred cycles, but in normal use, this will drop to a couple of dozen recharges at most.  A risk with recharging regular (especially Duracell) Alkaline batteries is cell leaks, which I can assure you, definitely does happen.  :)


The Outspoken Wookie

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