Rechargable Batteries

Hi Folks. Just to save someone from a serious fire, please do not attempt to change standard subC nicd cells with LiIon. The most common LiIon size cells are so called 18650 (18mm dia, 65mm long) so do not have the same form factor as SubC. The real danger however is in the battery management system. This controls the charge as well as the discharge. LiIon cells should not be over discharged. While LiIon cells do not contain any free Li metal, they can form free Li metal if they do not have a proper battery management system. The main issue is fire due to improper charging. The electrolyte in LiIon cells is flammable, unlike Nicd or Nimh. Also with over charging and the cell temperature rises, eventually you get thermal runaway and oxygen is generated. So you have flammable electrolyte, self generated oxygen, making it very difficult to extinguish the fire.

Also having spent 15 years evaluation cells for the major power tool company, I will have to agree that DeWalt nicd cells are the best that are currently produced.

And just a note, if you elect to replace cells in a pack, the new cell connections will have to be spot welded. Soldering risks damaging the separator or the vent system.

Just want to keep folks safe. I have witnessed too many fires during abuse testing.

David
 
Wow thanks David!
Great tips- I have wanted to start replacing my cells, and may likely have considered "upgrading" to LiIon.

I have to ask you though- my chargers are meant for both LiIon and NiCad because they are Ryobi. They sell LiIon batteries now too, and both types of battery can go in one charger. D you think that is ok, since the charger is meant for both?
Unless the battery has some circuitry to tell the charger what type of battery it is... Hmmm..


Bernie
 
Bernie, I am not familiar with the latest Ryobi packs. However one of the differences between the battery management system (BMS) is that with LiIon there are usually cell taps off of each cell of the string in order to makes sure that an individual cell in the string is not over charged or under discharged. Nicds don't have that.

If the charger is designed for both types of chemistry, then it would be ok to replace cells, however again it is more tricky with LiIon since the entire pack should be balanced. And like I say in order to replace cells then the weld straps have to be spot welded. If you have a spot welder you can try.

As I read your post, if you are talking about "upgrading" a nicd pack to LiIon, then I would say no you can't do that. There should be some different connections and perhaps electronics in the LiIon pack that won't be in the nicd.

David
 
Bernie, as mentioned, don't replace the cells in your NiCad packs with Lithium. Check whether the OEM lithium packs will work in your tools. Most tools made for lithium have circuitry to prevent unsafe discharge conditions. The NiCad tools may have different dovetails or contacts to prevent interchanging the battery packs.

The charger may be the only component that's made for both.
 
I needed a new battery and the charger for B&D 14.4v unit. $45 battery & $55 for the charger. Looking around the store I found another kit - drill, saw, light with 2 batteries and a charger for $105. Guess which I bought. The new charger lasted maybe a year. I now use a different charger that is more robust, ie has a fuse, the batteries are not as strong as new and I was thinking of trying out the battery rebuild service that The Source offers locally.
Pierre
 
Can't speak for the Sears stuff, but I have been using the Ryobi for several years and have no problem with it. One of the things that made me buy it in the first place is the wide choice of batteries and other tools that use the same system - string trimmers, drills, impacts, saws, etc. NiCd or Li Ion. Batteries are a lot cheaper to replace as well, especially if you buy two packs. I am just about fully LI Ion now and love them. If you are using them around the house, they are just fine. If you are using them 8 hours a day, consider the Rigid line, since they will replace the batteries for free, if you register the tool and keep a copy of the receipt. Of course those options only work if you have a HD store handy. However, I'm certainly not saying DeWalt is bad....To get back on topic, you can use individual cells, but be sure to buy the kind that have tabs welded on them. You can pick your price range and capacity if you do rebuild them yourself. Last time I saw a sears battery price, I beleive it was pretty pricey, so rebuilding might work out well. I have bought cells from a company called All battery with good results. If you can solder, you can probably rebuild it yourself. Take a look inside the pack and you will soon know if you want to tackle it yourself or not. As for the temp sensor being used to determine full charge, I believe you find that most chargers use a voltage / charge current curve to detect full charge rather than temperature - using temperature is a good way to ruin a cell in a hurry bu over charging. The temp sensors are usually used as safety devices to prevent overcharging. Oh - and it's not usually a good idea to try to replace one or two cells, as this can cause other cells to over or under charge due to mismatched internal resistance of the old and new cells, since they are charged and discharged in series.

Dan
 
Sorry about the late response- VoltmanBatteries.com!! That's who I used and they were great.



Bernie
 
in my past business I serviced batterys for my contractor customers. I even built a battery "tab welder" with couple gawd awful big capacitors, diodes and switches. most of it fits in a empty computer tower. a fun project to say the least. actually I still have it. but it needs about 16VDC and I don't yet have a power supply that will go that high. two neat little probes and a foot switch to trigger the diode to zap the big capacators. quite a jolt that could cause serious harm.

I purchased the batterys pac's from a place in calif. that assembled the pac's and I just had to do a smalll amount of connecting when I installed them in the cases.

interesting idea I had, going into the rebuild business by obtaining the single cells and spot welding them in the proper array. . . cost on batterys was really low if ya wanted to spend a couple grand on batterys, so I abandoned that idea. but I did find the sources where they were reasonably priced.

I so realized that I could not compete with "batterys plus" or "interstate battery" without a big advertising campaign which is more than expensive.

prior to the tab welder I actually soldered the tabs on, using a big copper "club" type soldering iron heating it with a torch. the club got the part hot REALLY fast so you would not heat the part slowly with a little soldering gun and ruin the battery. I never had a complaint about that procedure.
 
I've rebuilt a couple of B&D 18V NiCd packs (which are crap) with lithium polymer cells salvaged from dead laptop batteries (I can hear people running screaming for the fire exits now!), which I test for voltage, capacity and self-discharge. Usually one or two parallel pairs has gone bad and tripped the pack PCB and the other pairs are often fine. Some packs are just plain worn out or have been left uncharged for too long, but about 60% of the 60+ packs I've torn down have had a duff pair.

Anyway, one pack was built 5S2P with ~3Ah cells for ~6Ah total capacity, the other pack was built 5S1P with ~2.5Ah cells. The first to have enough juice and discharge rate to power my strimmer (which'll rip through a NiCd battery in about 10 minutes), the second as a light weight battery for my drill/ vacuum/ palm sander/ hedge trimmer/ circular saw. They're interchangeable, with the exception that the large one won't fit in the vacuum as I had to make a little riser to fit all the cells inside. Both have balance taps wired to a balance plug glued into the housing and I use a voltage monitor to keep an eye on voltage during discharge (as pointed out above, over discharge kills lithium cells). I balance charge them using my RC hobby charger. They're both fantastic - either slightly more capacity and less than 1/2 the weight or over twice the capacity and the same weight as the stock NiCd batteries. They hold their charge for months and work fine below freezing (like last night), plus they hold enough capacity to be able to use them to do trail work - the large battery allowed me to reopen a 2-3mile section of trail with my hedge trimmer all on one charge (almost 3h of continuous use) - without having to lug heavy petrol powered tools into the woods.

However, all of the caveats mentioned above do apply - working with lithium rechargeables, especially unprotected cells, isn't for the foolhardy. They contain an incredible amount of energy which'll more than happily melt metal if you let it and they need extra care with charging. That said, I've found lithium batteries to be very robust and I've used them (mostly bike light batteries) in some very tough conditions without problems. If you're up for investing some money in a good charger (which can charge lots of other things), reading up on how to make packs and handle the cells, then I don't think it's that big a deal.

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