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'C' cell batteries, unusual...

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HarveyH42

Banned
I just change out some batteries, Duracell alkaline 'C'. Test them to see what they had left (great for the Joule Thief). Two of them measured 0.8 volts, the third was -0.79 volts. Checked everything several times, it's no mistake. The polarity on that one battery is reversed. I don't know how happened, but the batteries were low, but not dead, when I through the thing on a shelf, about a year ago. Figured I'd better pull the batteries, kind of expected some leakage. Batteries look fine, no discoloration or swelling, no mess to clean out.

Anybody ever run across something like this before. Kind of strange. Little concerned, as the batteries I put in are NiMh and a little pricey for a dog toy anyway, kind hoping that damn mechanical cat doesn't mess one up.
 

smanches

New Member
Not uncommon. That cell died way before the others, and they basically charged it backwards.

Used to see this quite a bit in RC car battery packs. Always had to remove bad cells and rebuild the packs with good ones.
 

Sceadwian

Banned
Cell inversion happens when one cell discharges before the rest and current is forced through that dead cell from the rest that still have charge. You said the batteries were Alkaline C's but then you said the batteries you put in are NiMh? Cell inversion will happen with any battery that is discharged and becomes imbalanced in a pack like that, solution is don't discharge them so deeply, don't mix cells from different packs, and keep the cells topped off. If they're alkalines, don't discharge them so deeply in series like that, and don't leave them in the device when they're not in use, self discharge in an unused battery pack will often cause cell inversion and leakages from Alkaline cells.
 

Sceadwian

Banned
Looks like me and smanches posted at the same time. One thing though... NEVER 'rebuild' a rechargeable battery pack. If you have 4 rechargeable batteries in a pack and 1 inverts, NEVER replace it with a fresh battery. This will cause the pack to become imballanced and pretty much garuntee that the weakers cells are going to invert later. This can cause fire/leakage hazzards under the wrong conditions, especially with rapid chargers.

If any cell in a pack inverts you should dispose of the whole thing and make a new one from fresh cells. Cell inversion doesn't happen if you use good charge/discharge practices and always constructs long serial packs from batteries that are as close together as possible in line from the maker. Preferably one right afte the other off the assembly line.
 

HarveyH42

Banned
I pulled the alkaline, replaced them with the rechargeable, only 'C' cells I had on hand. It's good to know, and will pull them after the dog get done killing kitty...
 

audioguru

Well-Known Member
Most Helpful Member
Energizer C and D Ni-MH cells have a tiny AA cell inside. It lasts longer than an old C size Ni-Cad cell.
 

Sceadwian

Banned
I think it's cheap that they did that, you'd probably get a lot more capacity out of a C or D battery if it were a properly designed cell rather than repackaged smaller cells.
 

smanches

New Member
I had a ni-cad cell matching charger that I used to let me know what cells I could use together to rebuild packs. It's a very common thing in RC car racing. Especially when a 6 cell pack can easily cost over $100.

How are NiMH batteries at self discharge? That's the one thing that are great about alkalines is they have such a low self discharge that you can keep them in a device for years and they still work.
 

Hero999

Banned
Energizer C and D Ni-MH cells have a tiny AA cell inside. It lasts longer than an old C size Ni-Cad cell.
Don't buy energiser.

All the C cells I have are either 4500mAh or 4000mAh.

I have a couple of 9000mAh D cells.

None of the above are Energiser.
 

HarveyH42

Banned
These are Tenergy brand, 5000mAH. They have the 'Made in China' label, so they must be good :). Had them for about a year now, and no complaints.
 

audioguru

Well-Known Member
Most Helpful Member
My Energizer Ni-MH cells say on the label, "Made in Japan for Energizer". Maybe Sanyo?

One of my solar garden lights came with an AA Ni-Cad cell that has the metal on its end caps so thin that it peels off like paint. It doesn't say where it is made but Google has a link to its Chinese manufacturer.

New Ni-MH cells have much lower self-discharge than before. They advertise that they are charged when you buy them. Their capacity is slightly less than before.
 

Sceadwian

Banned
With Cadmium being on the environmental hit list and NiMH's being all around better I'm surprised they still use them. all the solar lights I've taken apart have Nicads in them.
 

Hero999

Banned
Nicads can supply higher currents, not that this is important for LED lights of course.

It seems odd, maybe Nicads are still cheaper or they're using up large stocks of them.
 

Sceadwian

Banned
I hope not, because batteries do go bad on the shelf.
 

audioguru

Well-Known Member
Most Helpful Member
Ni-Cads are cheap todaty because they make them or store them in China. They don't know or they don't care that Cadmium is a deadly poison.
 
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