Introduction and Backstory**:
Introduced in 1993, the Rayovac corporation marketed and sold a rechargeable battery system dubbed "Renewal". It was unique because it used a rechargeable alkaline battery which is very similar to a regular "disposable" battery and it promised to fill the gaps that the nature of "normal" rechargeable batteries left. They had a several year shelf life compared to at best a few months, fully charged they offered the same 1.5 volt power as normal alkaline compared to the 1.2 volts of Ni-Cd or Ni-MH batteries and of course were much environmentally friendly because they were basically alkaline batteries that could be recharged, no heavy metals or toxic materials requiring special disposal.
However, you had to buy a special "smart" charging unit AND fairly expensive special batteries that only lasted 20-50 charging cycles as the capacity dropped rapidly with each charge. Add in that those special batteries were notorious for leaking which often ruined both the chargers and the devices they were used in. Needless to say, the entire system was not well received met with discontinuation around 2000(?).
Still many thousands of chargers and batteries were sold in the USA. I happened to be one of those that bought both the chargers and the batteries and used them for a very long time.
Finally, however, I just retired my very last Renewal battery a few days ago. This left me with not one, but 4 Renewal branded chargers that were now utterly useless due to the lack of rechargeable Alkalines and the fact the early model chargers I owned could not be used to charge regular Ni-CD or NiMH batteries! (Yes, I do know they are still KINDA available under different names, but they suck, just like back then)
What to do? What to do...
**To get to the good stuff where the magic happens and avoid all this long winded nerdy cruft, skip ahead to step 2!
Step 1: Information, Information, Information...
To think of a solution, first you need to find a problem!
Now, due to the limitations of regular rechargeables, I still use disposable alkaline batteries in a few places in my house in devices like flashlights, my wireless keyboard, remotes, clocks and a "emergency" back ups for when a rechargeable died and I didn't want to wait for them.
As you can see, most of those devices have a fairly low to extremely low battery "turn over" rate and hence my "stock" of alkaline batteries is very small and I often have none or run out when I need some fresh ones.
Problematic no? Yes! Not to mention expensive and hard on the environment!
Well I have long known about these special chargers for regular alkaline batteries that could "top off" a normal, non-rechargeable battery and give you some more use from an otherwise "dead" disposable battery. The problem was I didn't want to buy yet ANOTHER charger to go with the stack I already have for Renewals, just NiCad's, just NiMH's and of course NiCd AND NiMH's...
No joke, I have 11 battery chargers in my house. So, another one was NOT welcome.
Still, I was curious about the concept and spent some time poking through the internet for tidbits on the interesting idea of doing something that was not supposed to be possible, or even attempted according to the warnings on disposable batteries...
There is surprisingly little solid information about the whole concept, but I mostly found that it could be done and done fairly safely if you followed some basic rules, used a custom built charger and baby sat it... Oh goody! I won't need to buy another charger, I LOVE building electronics AND I can use one of these old useless renewal chargers for parts! Whee!
Wait... I'm going to build a charger to recharge alkalines... I HAVE a charger designed to charge rechargeable ALKALINES... What the heck is the difference?
Turns out, not that much.
About half an hour of research on Google, Rayovac.com and Wikipedia, left my lazy side grinning like an idiot. Between rechargeable alkalines and disposable alkalines, there were minor differences in chemistry so the rechargeable variation would take a charge better and repeatedly, along with better leak protection... In short WHAT difference?
I grabbed my tools and I found, to my delight, that the Renewal charger uses a low average current (~20-40ma) provided by 2 volt pulse at a 50% duty cycle... According to the information I've found that's practically PERFECT for charging a regular alkaline! It's even got a "full charge" cut off at 1.7 volts, a bit high, but I wouldn't even need to baby sit it when it was charging! Besides, if a battery blew up, no big deal, I had 3 more and the charger was useless anyhow!
I could Reduce, Reuse AND Recycle all at once! At this point I was happy enough to start crapping electrons.
Figuring I should be able to stuff a regular alkaline right into a Renewal charger and be good to go, I grabbed a near death battery from my remote control and popped it in to witness the astonishing act of... nothing.
Back to my tools and a closer examination. Turns out the battery wasn't making a connection because Rayovac designed a safety system so people couldn't do exactly what I was trying. (ref: http://www.rayovac.com/technical/wp_batoptions.htm -Near the bottom above Fig. 6 after lots of marketing propaganda and useless fluff)
Now, if there is one thing I have learned in life (often after regaining consciousness) the best part about safeties, is finding ways to get around them ;)
Lets get crackin'!
Step 2: Renew and Reuse Your Renewal Charger! (Simple Edition):
"D@mn the torpedo's! Full Speed ahead!"
The "safety" system implemented by the Renewal charger is pretty simple, it charges on the VERY outside rim of the positive terminal ("nub"). Now, >99% of modern disposable batteries have a plastic sticker that covers where the Renewal charger tries to make contact in order to charge the battery.
So, the simplest solution is to take a fingernail or knife and just peel back/off the sticker to reveal the more of the positive terminal underneath. See my pictures below.
Beautiful! The whole thing works without any more effort and lets you breath new life into dying batteries with only the slight risk of breaking a nail!
Was I satisfied? Heck no. It's a pain in the butt to modify EVERY dying alkaline I want to give a boost, especially when you can only charge them about 5 times with diminishing returns before they're useless or leak!
This won't do at all.
Not only am I too lazy for that amount of fiddly work, I'm also enough of a nerd that I shouldn't have to put up with such annoyances!
Lets move on to a more advanced solution! *
*Warning, advanced solution is not for people who get squeamish at the thought of taking something apart that uses mains voltage!
Step 3: Renew and Reuse Your Renewal Charger (Advanced Edition!):
Lets get to work on making this old piece of crap more useful.
As we know, the culprit in this dilemma is the positive charging terminal, the design avoids any contact with an area that is exposed on a standard disposable alkaline. So to ensure we don't have to fiddle with modifying EVERY battery we want to recharge, the solution is simplicity in itself. Modify the positive charging terminal for all 4 slots!
(Images are below in order)
1.) Remove the single screw in the back of your Renewal charger.
2.) Now we need to pry it apart. Start at top of the charger where the screw was an work your way all the way around. I suggest a putty knife or thin screwdriver and not a pocket knife as shown, I am an idiot and am trying to cut off my fingers.
3.) After getting it open, the part we need to fiddle with is highlighted in the picture.
There are a number of ways to approach modifying the contacts once it's open, but I'm going for lazy here.
4.) Grab a trusty pair of pliers and take hold of the contact and bend it down "into" the area where the battery would normally sit when charging and then flatten it out so it'll fit back through the case. This effectively moves the contact point from the outside ridge of the battery to the middle (ish).
5.) Re-assemble and use. Perfect! It works great!
After the modification, initially inserting a AAA sized batteries was a bit difficult but after the contact was "formed" (aka bent) by the pressure, they popped in and out easily.
Now for the best part! Grab some dead batteries and charge 'em!
Step 4: Results Anyone?
******ZOMFG MAKE SURE YOU READ MY DISCLAIMER!!!!!!*****
I'm sure anyone who might be still interested is wondering how well this process works and just how safe it is before they risk damaging their obsolete equipment and potentially blowing a hole in the wall.
I'm pleased to say that it works surprisingly well! The batteries don't even get warm from the charging process, however the charger throws a lot of heat that warms them up but no big deal.
From my own experimentation, the LESS dead the battery, the more it can benefit from recharging.
Cells that are down to around 1.2 volts recharge brilliantly and can be cycled around 10-15 times before their capacity (life) was shortened to the point of uselessness. When charged from this point, I have not had a SINGLE cell leak while charging it or during use (see the catches below)
Cells that have been brought down to the modern standard of "dead" at 1 volt, DO charge ok and can survive several charge cycles (best is 7 so far) but their capacity is severely diminished each time and rapidly become useless after just a few charges. I have also found that these batteries are far more prone to leaking and have had two leak on me when charging during my testing, both after 8 cycles. I haven't had one leak in a test device yet... (PLEASE read my catches section!)
Some numbers about the status of the batteries post charge for the nerdy types like me:
Charge termination voltage: 1.7 volts (drops to around 1.4 after 3 hours, no further drop has been noted. A second cycle brings the "rest" voltage to 1.55)
Initial new test cell voltage: 1.62 volts
New generic test cell capacity to 1.2V, 200mah discharge rate: 2300mah
Post charge capacity to 1.2V, 200mah discharge rate: 1400mah (1 cycle) - 350mah (@7 cycles)
Post charge capacity with doubled charge cycles to 1.2V, 200mah discharge: 1700mah (1 cycle) - 500mah (@7 cycles)
Sorry, I don't have fancy computer data collection hardware or I'd post some charts up! Lemme know if you want more charge/discharge info!
There ARE a few catches to using recharged alkaline batteries so please read the following!
1.) As you can see the capacity is NOT going to be the same as a new one and drops off rapidly with each cycle.
With a single charge cycles, the Renewal charger shuts down when the battery reaches 1.7volt, however as the battery "rests" the voltage will taper off over the course of about 3-5 hours. I find it usually settles at around 1.4 volts. At this point I pop them back in for another round. it seems to maximize their capacity and usefulness after being charged AND doesn't seem it have much impact on how many charges they'll take. You'll only get about 5-7 cycles out of any battery brought down to 1 volt regardless of using the technique or not, so why not make each cycle count?
2.) Recharged alkaline are much, MUCH more prone to leakage. DON'T use them in expensive or irreplaceable devices OR devices that will sit around unused for a long time!
***New Information Update! (5/2/2010)***
3.) Recharging "AAA" size batteries if they are under 1.2 volts or under is now "officially" discouraged due to a failure rate I would consider "very high" and have even had one cell (started at .8 volts) vent it's electrolyte with enough force that I heard the "pop". This charger's current is a bit too high to recharge AAA's safely.
4.) Recharging ANY battery that is OLDER than 2-3 years AND/OR has a terminal voltage of 1 volt or less is now considered a "bad idea". I have been getting a 5%+ fail rate for the seals days or weeks after charging causing them to leak in the device they are being put in. New batteries or ones over 1.2 volts have very rarely suffered these failures.
5.) "High performance" alkaline batteries seem to charge better and retain more of their original capacity after charging.
******READ MY DISCLAIMER AND SAFETY TIPS ON STEP 5 (OR BELOW!)!!!!!!*****
Step 5: ***DISCLAIMER!!!***
>>>YOUR ATTENTION PLEASE!<<<
This instructable is for your personal use and instructs you on how to do things you are EXPLICITLY WARNED TO NOT DO by the battery manufactures, by a warning AND safety system on the charger, even on the batteries themselves!
Myself, instructables.com, Rayovac or any manufacturer of battery that you attempt to recharge are not, and WILL NOT be held, responsible if, by following these instructions and using the modified charger and/or batteries; you burn down your city, blow up your house, cut off your fingers, set your cat on fire, damage your charger, get a computer virus, destroy the electrical wiring in your home/apartment, kill your houseplants, destroy your batteries, tear a hole in the ozone layer, make a wrong turn at Albuquerque or ruin your devices that you've used your recharged batteries in.
Other than that, have fun recharging! Just don't come crying to me if it all goes sideways! These instructions are more or less "as-is" with no warranty or "110% satisfaction guarantee". If you have a problem or question, I'll gladly help if I can, but I'm no miracle worker :)
1.) The alkaline solution (It's a BASE not an acid!) is fairly weak and reasonably non-toxic. It's harmless so long as you don't try and drink it, keep it our of your eyes and wash it off your skin and any surface it's come in contact with (like the inside of your charger) using a clean damp rag with relative prudence. A few minutes of contact can lead to skin irritation, so rubber gloves are NEVER a bad idea when handling leaking batteries!
2.) I haven't had any batteries fail in a "spectacular" way such as detonating, rocketing across the room, spraying acid in all directions, melting a hole into the basement or forcing me to whistle "Row, row, row your boat" while going naked through a car wash, but it doesn't mean that it's impossible. The renewal chargers have a plastic cover that I'd highly recommend that you keep CLOSED while charging in order to help guard against freak accidents. Supervision and not letting them charge unattended is never a bad idea also!
3.) Do NOT, and I repeat, DO NOT attempt to recharge regular Ni-Cd or NiMH batteries in a renewal charger modified or otherwise! They WILL fail and probably leak! End of story!
4.) Never, ever, EVER, EVER try and charge ANY disposable battery with the word "Lithium" in the name in this charger or any other! (i.e.- Energizer's Ultimate Lithium) it won't work and you're risking your safety. Rechargeable Lithium batteries, of course, exist, but NEED a special charger. This charger, modified or factory, is NOT it. This is not a joke. This is not up for debate. Do not even be curious about what happens. DO. NOT. DO. IT.
4.) This is a repeat from my "catches" section, but it bears repeating. DO NOT TRUST RECHARGED BATTERIES! The electro-chemical process from charging an alkaline puts a high amount of stress on the cell and makes them far more prone to leaking! I haven't had one leak when NOT charging yet, but, just DON'T use them in expensive or irreplaceable devices unless you understand and accept the risks!
5.) Enjoy sticking it to the man AND keeping more batteries out of landfills!