D.I.Y from the dark side of the net :) ( Recharge Dead Batteries) :)

[JT]

http://www.i-hacked.com/index.php?option=content&task=view&id=207

[Peter Snowberg]

There are actual rechargeable alkaline batteries out there, but they're NOT the same as the disposable batteries you get off the shelf.

Recharging a cell that was not designed for it is BAD NEWS. I have personally witnessed a 9V alkaline explode with pretty decent force; enough to blow the metal wrap off and crack the thick plastic case it was in.

This is a classic case of being able to "get away" with it most of the time.

The benefit is not large and the potential danger is very real.

Stick to REAL rechargeables.

[R.G.]

I personally drove one of my employees to the emergency room to get his eyes flushed out and tended to when he accidentally vented an alkaline battery and it spewed battery gook into his eyes.

Death and disfigurement is one thing, sight loss is quite another.

It is true that alkalines can be recharged sometimes, for a while. Sometimes it works fine. Sometimes they go off. It's not worth it.

A true tinkerer would put the batteries into a modestly explosion proof box or do it outside, eating up any savings. It's still not worth it.

[Joecool85]

Yeah, I was thinking about doing it, but for the price of batteries...I dunno, you'd have to go through a lot of batteries to need to bother doing that.  On top of that, like you guys said, get actual rechargeable batteries!  It is still a neat idea though.

[JT]

Figured as much..pretty cool site though

[Paul Perry (Frostwave)]

During WW2, when shortages were pretty severe, there was a lot of amateur work done on recharging carbon/zinc batteries. the consensus was, you could extend life significantly. Plus, the charging was best done using pulses.
But, I wouldn't bother, personally.

[Mark Hammer]

With two guys I respect deeply offering contrary comments, I will preface my own comments by saying I am uncomfortable making these comments below.  Let me also emphasize that you should not do this unless you are attentive, vigilant, well-protected, and know what you're doing.

Okay...I regularly recharge both alkaline and carbon-zinc batteries.  Been doing it for years, and will continue to do it.  With some 50+ pedals sitting around that  use 9v batteries,  pulling cheap batteries back from the brink had natural attraction to me, as you can expect.  A couple HAVE overheated and popped, but they have done so under the cover of my Ni-Cad recharger.

This, however, is th "big but" that separates the successful from the partially blinded and disfigured....

Carbon-zinc and alkaline batteries behave differently than true rechargeables so you can not use the same strategy you would for these nonrechargeable types.

How do they behave differently?
1) Ni-Cads will self-limit during charging.  You can leave them plugged into the charger for days and nothing bad will happen.  NOT so with alkaline and carbon-zinc.  They WILL pop. They've only made a small noise and bulged in my experience with several hundred of them, but if pewople say they explode, BELIEVE THEM.   I would not dream of leaving them plugged into my charger for more than an hour at a time.  The issue is heat build-up so you can always unplug and give them another hour sometime later.  If you have plans to rejuvenate a 9v alkaline or carbon-zinc, you CANNOT be watching the Superbowl, helping your kids with homework, expecting a call from the autobody place with an estimate, or doing anything that would conceivably distract you.  If you can't guarantee those conditions, don't do it.  I only charge mine when I'm sitting here doing something like this and the charger is a few feet away where I can feel the batteries and avoid any heat build-up.

2) Ni-Cads charge better when they are almost drained.  If you try and recharge a Ni-Cad from 7.5 volts back up to 9v, you likely won't make it.  The complete opposite is true of carbon-zinc and alkaline.  If the battery reads less than about 7.5, don't bother.  Just use it for a homebrew battery snap (http://ampage.org/hammer/files/DIY-snaps.pdf).  IN some respects, it might be more proper to call what I do to older batteries is to "perk them up" with a shot of current.  A lot of the batteries I've done this with are industrial Duracells that I've gotten from institutions that dispose of them once they drop below 8v or so.  In some cases, they don't even measure them, but just dump them after some fixed period of service.  I can easily bring them back from 7.4v to a healthy tongue-tingling 9.5 and sometimes even 10v with just an hour here and there. 

Keep in mind that "recharging" such 9v batteries will NOT provide the lifespan that a new 9v battery has.  In fact, the battery can often lose a half volt from maximum charge just sitting there on the counter overnight.  If you're building something and you want to stick some power in without having to snag a battery out of something else, this works fine.  In my own case, my "re-use policy" allows me to have a lot of batteries in a lot of pedals that I use very intermittently.  They may be 8.8v just sitting there, rather than a punchy 9.5v, but I'm not expecting them to last through a 3hr gig either

So, in sum, if your needs are like my own, giving some older 9v you had hanging around a little jolt to breath a little bit more life into them until you get to the bargain store for some more batteries, it WILL work.  When it comes to safety, though, don't monkey around unless you know what you're doing.  Pete and RG are right.

[Peter Snowberg]

I've never used any of the actual rechargeable alkalines, but I see references to them being charged 25-100 times. Apparently the chemistry isn't too much different from regular alkalines.

If I were going to deal with recharging (I used AC most of the time), I would just get high capacity NiMH cells and a smart NiMH charger chip from Maxim or Linear. NiMH cells are getting really good. 

Thanks for offering your empirical input Mark. I don't want to make it sound like the sky is falling, but when that 9V went off it was a bang that was louder than an M-60 firecracker. I'm very glad it was inside a plastic case!

Even if the chance is 1 in 1,000,000, if you're that 1, its 100%.

Be careful folks.

[Twister22]

I recharge 9v batteries by leaving them under a quartz pyramid.  They almost always blow up. 

[Peter Snow]

To add another perspective:

Many years ago I bought an alkaline battery charger called the "BuddyL"    It will re-charge most cylindrical alkaline batteries (AAA, AA, D, C etc) but unfortunately there is no provision for the 9v type we have come to know and love.  The good thing about this device is that there is an LED above each of the four bays which light up amber for a good battery that is being charged, green for a charged battery and red to indicate that the battery cannot be charged for whatever reason (too low a voltage to start with?).  There is a definitive charge cycle which appears to be based on time and voltage reached, so I feel confident in loading in the batteries and leaving them to charge, unattended.   

The instructions echo what Mark said about "topping up" batteries before they become discharged too much.  I have used this for many years with no problem at all and I imagine I have saved quite a bit of cash doing this, not to mention the environmental benefits.

Sadly I believe they are no longer available - though I have not really looked for them recently.

Just my 2c.

Peter

[GFR]

I blew up some alcalines once. It totally ruined my NiCad charger. Fortunately, the cover avoided further mess.

Don't ever dream trying this in a charger without a cover and for safety place the cover away from curtains, etc.

[brett]

Hi.
I bought some rechargeable alkalines a year or two ago.  My 10 year old has a radio controlled car that eats batteries, so I thought that a life of 20 to 50 re-charges they would be great.  But they're not nearly as good as they sound.  First, they're more expensive than regular alkalines.  Then, you HAVE to recharge them while they still have a fair bit of charge (>50%).  My son ran them down until they were dead a few times, which I think shortened their life.  I reckon I only got about 10 full charges out of them. 

Go for nickel metal halide batteries.  Their cost has got really low (in Singapore, China etc you can get factory rejects for $1), and their charge capacity is super high, and the number of recharges is so high (hundreds), and they have no "memory" and can be recharged from nearly full or empty.  Goodbye disposables!

cheers

[Joecool85]

Actually, NiMH batteries do have memory.  Not as bad as NiCad, but still, they do have it.  Li-ion doesn't really have a memory though.  But good luck finding some 9v li-ion rechargables.

[George Giblet]

Well I can't agree with all the doom and gloom.   The fact is Li-Ion batteries have similar problems to rechargable alkalines, and Li-Ion batteries are popular (despite being far from perfect).  Did you know that Li-Ion battery packs have circuits inside the batteries to protect them?  Did you know that devices containing Li-Ion batteries above a certain weight are not allowed as hand luggage on aircraft?  The thing is Li-Ion offers the advantage of higher power density, and they cost more, so people are willing to pay for the necessary layer of protection to take advantage of them.   Without that addition they probably couldn't be put on the market.

> My 10 year old has a radio controlled car that eats batteries, so I thought that a life of 20 to 50 re-charges they would be great.  But they're not nearly as good as they sound.  First, they're more expensive than regular alkalines.  Then, you HAVE to recharge them while they still have a fair bit of charge (>50%)

By the same token my father had the same set of Rechargeable alkalines for several years running camera flashes and a mini radio cassette.  He got excellent life out of them.  I think rechageable alkalines don't perform that great with high loads like RC cars.  In fact with very high loads like RC cars NiCd batteries can actually get longer run times than NiMH batteries of higher capacity.  This is well known.  It's to do with the fact NiCd have lower internal impedance and hence have lower voltage drop for a given load.    You have to choose the right battery for the job.  Checkout ,

http://mygrandcell.com/faq.html

It mentions the preference for low drain applications.

The same applies to charging normal alkalines, perhaps more so.

It is possible to build better and safer chargers for alkaline batteries.   IMHO the battery brand has lot to do with the success and freedom of rupture.  The comments Mark made agree with what I have found (I would add that *all* battery types drop off in voltage when left after charging). This guy says similar things

http://www.repairfaq.org/ELE/F_Battery_info.html#BATTERYINFO_007

Charging series multicell batteries, like 9V's, presents more of a problem regarding overcharging and safety.  This too is a problem for Li-Ion batteries and solutions are available for chargers - the idea won't work on *commercial* 9V alkalines though.

I say go forth and charge, it does work, but don't take chances.  Keep the batteries away from people and charge them where they won't damage anything if they leak.   Don't use fast NiCd/NiMH chargers.  Use a slow NiCd/NiMH provided you go paranoid like Mark.  Use relatively low currents.  The chargers on the OP's link are no different to slow NiCd/NiMH chargers so treat them as such.