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Quote:

Originally posted by Joe Bloggs It makes sense if the electricity you use to charge your batteries costs $100/mAH Really--NiMH give you longer life, waste or no waste--what's not to like? And BTW, it's not a good idea to put batteries into storage after they've run flat, right? Charged batteries last much longer in storage than flat batteries right?

For long term storage it is recommended to store them flat actually, since the very slow self discharge can also induce some crystal formation. NASA if I remember correctly recommends draining NiCd cells al the way down to 0V (don't try this with your cells) per cell for long term storage.

About the waiste, sure it costs you nothing. My point was that if you look closely you may see that NiMH are not at all that superrior as the hypes claim. It is not for nothing many proffs still use NiCd and we are not talking only high drain here.

 

[fredpb]

My Rio 800 mp3 player has a nimh rechargable AA in it.
The RIO 800 has a feature called "Battery Calibration" It deep cycles the battery automatically. Takes about 5 hours for the full cycle (charges it too). SonicBlue support said if you use the 800 regularly you should do that once a week.

I had a new 74 VW Beetle. After a few years, sometimes the starter would be slow, so I would park on top of a hill and leave the lights on to discharge the battery. When the lights went out I would just push it down the hill, jump in, and start it with the manual transmission. Drive it around a bit, and the battery was like new.

My AA's are usually used in groups of four. I designed and built a four AA cell discharger for myself to cycle new batteries and regenerate old ones. It just discharges, not a charger.


I basically use a small relay in the discharger, and the discharge component is an LED and resistor. When the voltage reaches a certain point (usually when one cell goes almost dead) the relay kicks out and the discharge cycle is done.

You learn a lot about battery behavior with the Nomad Jukebox (1) and it's pain in the ass battery life

.

 

[Joe Bloggs]

Lead-acid batts should not be stored FLAT... NiCd and NiMH batteries should not be stored FULL??

ARRRGH

*pulls hair*

 

[fredpb]

Just for grins, more expert opinions, and again, they vary......

http://www.thomas-distributing.com/m...-batteries.htm

 

[}{azard]

Quote:

Originally posted by blr The problem with packs most often is bad cell matching. Your charger measures all these values for the whole pack. At the same time one (or more) individual cells may be weaker than the rest and thus not perform properly. The probability for this increases with increasing the number of cells in the pack. It is not that much of a problem with only two separate cells used for portables. After all you can (and should from time to time) cycle them separately. Draining any rechargeable cell fully before recharging only shortens the number of cycles, i.e. your packs will not last as long.

LOL! My packs are matched very, very well. When I pay 80 dollars for each of them, I expect them to be. They are matched to 1/100 of a volt, AIR is always exactly the same, and all the cells are within 2 seconds of each other for discharge time.

Josh

 

[}{azard]

http://64.70.208.72/speedtechrc/88.html

 

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Originally posted by }{azard LOL! My packs are matched very, very well. When I pay 80 dollars for each of them, I expect them to be. They are matched to 1/100 of a volt, AIR is always exactly the same, and all the cells are within 2 seconds of each other for discharge time. Josh

OK they perhaps were when they were new, but no way different cells in the pack can age differently. Sooner or a later mistmatch occurs. Plain and simple you can never get the same cycle life out of a pack compared to a single cell under same conditions. This has been verified experimentally.
One simple(st) reason you may think of. How is your pack positioned? Perhaps some cells are closer to heat sorces (engine) than others and run hotter-there you have it. Just an example.
Now, the discussion about racing packs is irellevant here. We are talking much higher drains, different cell size, and use.

 

[}{azard]

Of course it is irrelivant, but the point I am trying to make is that nicad cells do have a cell memory. It may not be as prevailent in PCDP batteries, but it is there.

 

[Ruahrc]

OK I need to jump in the fray here:

First I'm wondering about battery storage/care. I have the MS Wireless Mouse (Uses AA batteries) and I was thinking of buying a set of 4 1700mah NiMH's to use. They come with a 14-hr charger, which is really good (compared to the "rapid chargers" that kill your batteries). I'm just wondering what to do with the backup set. Should I charge it up after it dies, and store it charged for later use, or should I top it off before I use it again, or should I store them dead until I need them, at which point I will charge them up and use them?

Or should I go for a set of NiCd's because of the whole "slower discharge" thing? The claim is that the mouse will operate for about a month using Alkalines, and unless you're using it almost constantly- it's a pretty low-drain device. I wouldn't really mind having to replace my NiMH's a little more often just as long as it wasnt like every few days or so... 1700mah vs 650 (the highest I've seen for NiCd AA's) is a big difference. Slow discharge or not, 1700 is near triple the capacity.

Do they sell Li-ion in AA format? Or anything of the like?

And now for general battery care: Say I have devices with NiMH batteries (PCDP and Rio800). I should (and do) use them in full-charge cycles vs topping them off after just a little use right? Now say I have Li-ion battery-powered devices (m505 PDA and soon-to-be iPod). Do I use those in full-cycle or does Li-ion fare better with frequent top-offs?

Ruahrc

 

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Ruahrc

To answer your first question. Generally for such low drain devices (mause remote clock etc) rechargeables are not recommended. You wont save much money and the low drain plus self discharge is not so good for the cells eighter. About the slow overnight charger, it is a farly safe device, meaning that it won't destroy your cells quickly, but it is not the best solution. First of all, these are usually "dumb"chargers, having only a timer to terminate the charging. No matter how deep your cells are discharged (see below) the charger always keeps the current on for say 14 hours, means partially discharged cells get overcharged. Second, rechargeables (except SLA) generally respond better to quick charging. The slower the charging (and discharging) the larger the particles that form on the electrodes and particularly on the Ni one. I won't go deep into this, but NiCd and NiMH generally charge better at currents between C/3 and C. The problem with quick charging is that you have to have reliable charge termination method. Quick charger with only timer is BAD. You need a charger that will properly sense the battery state of charge and terminate once the battery has reached full charge. -dV technique is fairly good and modern chargers can apply it even for NiMH batteries, which have lower voltage drop at the end of charge compared to NiCd. IMO, the best plug in charger on the market today is tha Ansmann PowerLine 4 Traveller. Charges 1-4 AA or AAA cells while separately monitors each cell. You can charge different cells together. Works with both NiCd and NiMH chemistry. It will safely charge a high capacity NiMH cell for about 2,5 hours. In addition it works anywhere in the world. It ain't exactly cheap but it's worth every cent.

About your second question. Deep cycling any type of battery only shortens its life. You don't need to deep cycle your NiMh cells every time. If you don't overcharge them severely, an exercise cycle is needed once in a while (say once every 20-30 cycles). The problem with most PCDP and other portable gear is that the in-build charging circuits are usually dumb, i.e. timer controlled. Thus you face the choice of eighter overcharge a partially discharged battery or drain it flat and charge it. In both cases the lifetime of the cells is reduced. That's why people get so short lifetimes of say their gumsticks. Not many of these expensive cells survive much more than 100 cycles, whereas if cycled properly the cell will be good for at least 200-300 cycles to nearly full capacity.

Hope this helps.

 

[martioz]

About lithum in AA size click on this link
http://www.rswww.com/cgi-bin/bv/brow...oid=-667649491

Is this what you want?

I am looking for Size F NiMh in Australia for my custom battery pack, D size is not enough for me

I have moved from NiCd about two years ago and... I don't regret this decision

 

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Originally posted by martioz About lithum in AA size click on this link http://www.rswww.com/cgi-bin/bv/brow...oid=-667649491 Is this what you want? I am looking for Size F NiMh in Australia for my custom battery

I think Ruahrc asked about rechargeable Li Ion in AA format. This one is a primary cell.
You won't find AA Li Ion cells simply because their cell viltage is too high.

 

[recephasan]

Ruahrc-
FYI:
I am using Sanyo AA NiCds. They have 1100 mAh capacity. They're light brown colored with red logo and black text.

 

[fredpb]

No, you should not deep cycle Lion's.

As far as devices like RIO800, you don't have to deep cycle them every time, just every few times.

 

[Ruahrc]

Interesting. I always learned that it was best to go C/10 for optimum charge. At any rate, using NiMH's in my mouse with the overnight charger may not be the best thing for them, but it'll work fine, right? It just won't be theoretically the best treatment for my batteries, etc. But would I need to store my spare set empty or should I charge it up and then store it until it is needed, and top it off before I use them again?

Perhaps I could consider using NiCd's instead or even biting it and paying up for Alkalines? (Think poor college student here

)

One last detail to clear up: What is defined as "deep cycle"? For example on my PDA I run it from about 4.11volts (full charge) to about 3.85 or so before recharging it. The minimum power-on voltage for the unit is 3.76V, with the critical (point at which the memory gets wiped) being 3.72. So it's down to about 30% capacity or so. Is it healthier to keep recharging it even though I only use it a little bit and the voltage is only at 4.09 or 4.07?

Ruahrc