Should the battery be drained completely before recharging?
I dont wanna shorten battery life if thats the case..

b

From what I remember they're using Li-Ion batteries which don't require discharge before charge. I have heard people say that you should do a couple full charge/discharge cycles in the very beginning, but that might be FUD.

Well, if they need that to be done then they certainly don't say so! My guess is you're right, that it's FUD.

-Zeke

FUD?

www.acronymfinder.com

Or, for a more thorough explanation, Jargon File entry for FUD. Probably used in a slightly different way here.

I don't get it tho. How can rumors about fully discharging before recharging be "First Unit Deployed"?

Me.

Well my new Nokia phone has a Li-on battery and all the manual says is "charge initially for at least 6 hours".

On the website it says "Li-on batteries should be given a full charge/discharge cycle for the first 3 charges. These first three charges should be for at least 12 hours".

I did like it said and I get 7 days standby. My friend with same phone, only gave it the 6 hours, and gets 4 days.

yea, despite the fact that they are supposed to have no memory, seems like you can really shorten battery life with improper charging, and since this one would be difficult to replace, id like to get the official word from Rob or someone from RIO on this..

b

If I may contribute here...

Most rechargeable batteries (NiCD, NiMH, Li-Ion) need a few "very full" charges (and not quite so deep discharges) cycles to fully activate or "set up" the battery chemistry, and thereby maximize the available capacity of the battery.

Once that has occurred, you maximize battery life and capacity by conforming to the appropriate charge/discharge needs of the battery type.

"Memory Effect", which could be better described as "voltage depression" during discharge, primarily affects NiCD type batteries. It occurs when slow/partial discharges followed by recharges causes the chemistry in the battery to partially crystalize, which raises internal resistance, and shortens the discharge time before the battery voltage reaches the lower limit for the device being powered. If the partially crystalized NiCd battery is then fully discharged, then charged, after a few cycles, the internal crystalization dispates, and most of the usable battery capacity is again available.

NiMh batteries are so much less suceptable to voltage depression that even when it has occured, the loss in capacity may not be noticed by the user (maybe only 5% capacity loss).

For most NiCd and NiMH batteries, the primary killer is poorly designed battery chargers. Many chargers continue to push substantial power into the battery after it has become fully charged. This continued overcharging causes chemical degradation of the battery chemistry, and is not reversable once the damage has been done. Frequent overcharging (which can occur even if the batteries don't feel "hot" in the charger) will substantially shorten the battery life and reduce the effective capacity.

If you are getting significantly reduced capacity and short lifespans from NiCd or NiMH batteries (even if you are recharging them before they are empty), you should suspect the charger is overcharging the batteries. If a few full discharge, then recharge cycles don't bring them back to life, then either the batteries are truely worn out, or the charger has done them in prematurely.

Li-ion batteries (which have impressive power density and light weight) are so sensitive to charge and discharge requirements that they are always managed by a very smart power management circuit, which relieves the user of concerns regarding the best charge/discharge strategy.

For Li-Ion powered devices, just use the device, recharge it when you want, and don't worry about the battery (other than _fully_ charging, and significantly discharging, the first few times to fully activate the battery chemistry.)

Cool, nice post, thanks. Everything I wanted to know about batteries and more.

Quick question following up on your excellent battery details (feel free to tell me if I'm talking poo - ).

When all is said and done though, aren't all recharchables stated as having a battery life of..... "x recharge cycles"?

Which means you will get better mileage by using up most of the available charge before re-charging rather than just topping up. Or am I using too much logic and not enough intelligence .

Cheers, Sim

Female Urinary Device?

Never keep a full charge in your Pearl battery for periods of time, this will cause its capacity to decrease by about 20% per year. Instead, when you don't plan to use it for a while, discharge it to around 40% - At this charge level, lithium-ion battery degradation over the course of the year is around 4%. However, be careful not to over discharge your battery before storage as deep cycling also reduces maximum battery capacity - Hopefully this should not be possible unless you disconnect the battery and manually discharge it.

When not using your Pearl, keep it in the fridge, but don't put it in the freezer as freezing it will also adversely affect the battery maximum capacity.

The best results are achieved below 10 degrees celcius, although most of the data available is at 25 degrees since this is around room temperature, temperatures above 40 degrees celcius appear to be bad for the battery, the ageing process is accelerated at temperature and not in a linear fashion.

Note that this is NOT the official Rio line on batteries, but the results of my own research on Li-Ion batteries in general.

When not using your Pearl, keep it in the fridge, but don't put it in the freezer as freezing it will also adversely affect the battery maximum capacity.

errrrr.... fridges, harddrives, electronics & condensation dont mix (when removing karma from said fridge for use) even if u wait for condensation to dry up before use I'd be wary.

Jai

Sorry, the 'keep it in the fridge' bit was not meant to be taken seriously.

I should be more careful about the risk of my posts being taken too literally.

when you don't plan to use it for a while, discharge it to around 40%

It is true that the optimal STORAGE charge level for Li-Ion is about 40% of full charge, but in practice this is hard to do.
I suspect most Pearl users would use the device often enough for this to not be an issue.

If you WERE to store the Pearl for a good while, I would suggest fully charging it, then run it down about half way, and store it in a cool, dry location. Then fully charge it before starting to use it when you put it back into service.

I would expect most users to fully charge the device when they have the opprotunity, use the batteries as desired, then charge it again. This would be the model the designers would expect most people to use, and with a properly designed Li-Ion battery management system, you should get good lifetime and capacity from the battery pack.

One note; if you run the batteries to exhaustion, it is a good idea to recharge them ASAP, as fully discharged batteries (Li-Ion and other types) will internally degrade if left in a discharged state for an extended period of time.

aren't all recharchables stated as having a battery life of..... "x recharge cycles"?

Rechargeable batteries ARE marketed that way, but the reality (as usual) is more complex.

Many rechargeable batteries fall short of their potential cycle lifespan, mostly due to cheap/badly designed chargers.
If you are using a poorly designed charger, that is likely to be the major factor in how long your batteries last.

With a good charger, you will get more service life from a NiCD or NiMH battery if you run it down farther between recharges (hopefully getting more hours or days of service from each charge).

On the other hand, if you over discharge the batteries between recharges, THAT will also reduce their capacity and shorten their lifespan.

Devices that use a multi-cell NiCD or NiMH battery pack often will operate until some minimum voltage output from the battery pack is no longer available (and the device turns itself off). If that minimum voltage happens to allow ANY of the cells within the pack (especially if those cells are not perfectly matched in capacity/voltage characteristics) to drop below the minimum allowed voltage per cell, then that cell is internally stressed and is aged more rapidly than the others in the pack.

Subsequent deep discharges will result in that same cell being the first to reach critical level, but the device keeps drawing power until the overall pack output drops enough, so the "weak" cell gets more beat up every time the pack is heavily discharged. Eventually that cell becomes so degraded that even a fully charged pack doesn't last long before the weak cell's output brings the whole pack's voltage output down below minimum required for the device to operate.

I would suggest, if you are trying to maximize NiCd or NiMH battery pack life, that you endeavor to discharge the batteries "most of the way" between charges, but not try to run them into the ground each time, and recharge them promptly and fully.

If you suspect your charger is of the variety that continues to push power into the batteries after they have been fully charged, then take them out of the charger shortly after they have been recharged.

"Fast" chargers that recharge a fully discharged battery pack in an hour or two SHOULD have some sort of indicator that they are done, and SHOULD also stop charging the batteries. Unfortunately, many chargers don't fully stop, they just back off to a "top off" or "trickle charge" level. If that slower charge level is pushed for more than 30 minutes or so, you are overcharging those batteries, and they will degrade.

"Slow" chargers, that take many hours to recharge the battery pack, are often very simple designs that push power into the batteries at a constant rate, regardless of whether the battery needs it. These are killers, as the battery spends many hours being overcharged.

Devices that use a multi-cell NiCD or NiMH battery pack often will operate until some minimum voltage output from the battery pack is no longer available (and the device turns itself off). If that minimum voltage happens to allow ANY of the cells within the pack (especially if those cells are not perfectly matched in capacity/voltage characteristics) to drop below the minimum allowed voltage per cell, then that cell is internally stressed and is aged more rapidly than the others in the pack

Multicell (ie most) packs do suffer from capacity mismatch purely due to manufacturing process tolerances, and this can cause problems for both charging and discharging.
The discharging problem is because the weak cell can go flat whilst the other cells are still capable of driving current through it. This screws up the cell chemistry and damages that cell, thus creating a viscious spiral. NiMH cells are more susceptible to this damage than NiCd.
The charging problem is because the only way to tell when a cell is fully charged is to monitor it's voltage throughout the charge cycle - it will increase steadily until charged when it will peak and drop off slightly. At that point any extra energy supplied to the cell is disippated as heat and damages the cell as it does so. With 6 cells of varying capacities, that peak is going to happen at different times. This means that the voltage drop of the weakest cell may be masked by the steadily increasing voltage of the other cells, and the weakest cell may thus be overcharged. The worst case scenario is that the charger misses every peak except the last cell, and every other cell is overcharged.
These two issues also have the side effect of limiting the pack's usable capacity to that of the weakest cell. For most applications this isn't a problem - we don't really care whether the Karmas battery lasts 18hours or 18 hours and 20 minutes. But in the world of competitive RC car racing every coulomb counts, people pay ludicrous money for 'matched packs', where each cell has been individually measured, and the packs have been constructed out of cells with very closely matched capacities. Obviously the better the numbers, the more expensive the pack.

the voltage drop of the weakest cell may be masked by the steadily increasing voltage of the other cells

I believe that many/most Li-Ion "smart" charging systems (and presumably the type incorporated in Karma) actually monitor the voltage of each cell in the pack. This allows the charger to be sure of not violating the fragile charge/discharge requirements of the Li-Ion battery type.

Of course, very few NiCd or NiMH packs are built with individual cell monitoring, and you are correct that many NiCd/NiMH chargers, even those with proper end-of-charge sensing, can overcharge one or more of the cells in a mis-matched pack.

The best one can do is not aggravate the problem by over discharging the pack, nor allowing a "dumb" charger to frequently/grossly overcharge the batteries.

SOME better NiCd/NiMH chargers can switch from rapid to trickle charging early (a little before the initial "fully charged" voltage sag would have occured), allowing a weaker cell to be fully charged, yet still top up the other cells using the mild trickle current, which if low enough can be safely disipated by the weak cell without further weaking it. That allows the stronger cells to eventually reach full charge.

Overall, you are correct that the weakest cell in the pack is the limiting factor, so the strategy must be to not aggravate that weakness further.

As a side note, some smart battery systems (and not just Li-ion) will recognize when a fairly full battery is reconnected to the charger, and won't actually allow the recharge, since the battery doesn't really need it, and the (unnecessary) recharge cycle would only serve to shorten overall pack life.

packs have been constructed out of cells with very closely matched capacities

On that note, the fewer cells connected in series (ie: the lower the overall voltage of the pack), the less troublesome cell mismatching is.

I don't know about current RC practices, but from a battery lifespan perspective, the best arrangement would be very few cells in series, and separate monitoring of each cell (or set of cells in series), with an electronic power management system to draw from each cell what it can provide, and aggregate the outputs (with voltage inverters as needed) to supply the load. That way, each cell gives what it can, and the power management system keeps each cell operating in its optimal range.

More complex to implement, but it would allow you to get all the power that is in there (minus parasitic losses in the power management and inverter circuits), yet not abuse the individual batteries, thereby maximizing lifespan.

Do any RC systems use a smart power management system in the vehicle?

Do any of them regulate (voltage boost) power output, such that MORE power can be delivered to the motor near the end of the race, despite the rising internal resistance of the batteries?

I don't know about current RC practices, but from a battery lifespan perspective, the best arrangement would be very few cells in series

Most (competitive) RC disciplines mandate the series cell count, and those that don't (drag racers) care about voltage more than capacity. I don't know whether a lightweight voltage aggregation system could be made with enough efficiency to be practical - people are dumping 3Ah packs in under 10 minutes (>6C rate), so it'd need to be able to sustain 20A with near 100% efficiency to be worth considering.

Do any RC systems use a smart power management system in the vehicle?
Do any of them regulate (voltage boost) power output, such that MORE power can be delivered to the motor near the end of the race, despite the rising internal resistance of the batteries?

Not much, with the trivial exceptions of voltage boosting for the radio circuitry itself (most important for 4 cell classes), and some newer speed controls have a voltage cutoff to prevent over-discharging the pack as a whole.

IMO the biggest hurdles for RC technology at the moment are the national and international governing bodies who seem to set the rules to protect the bigger vendors rather than to promote competition.
The biggest inefficieny in electric RC cars is the motor - ~50-60% efficiency. Until mobile phone and laptop technology recently pushed NiMH to the fore, NiCds were topping out at ~2200mAh, making the battery pack a huge factor in racing competitiveness - hence ludicrous pricing for matched packs. Recently NiMH has helped reduce that pressure, at least in the local or club levels. The air/boating RC scene have made significant moves towards brushless DC motors which boast ~85% efficencies, thus reducing (again) the pressure on the pack capacities. RC cars are lagging because brushless motors aren't sanctioned for racing.

wow, thanks for all the tech specs guys!! but getting WAY too technical for me..
all i really wanna know is.. For everyday use, should i drain my Karma all the way before recharging or not?
thats it

b

lol ok I didn't pickup on that... maybe cause It was between two serious parts of your post...

cheers,
Jai

Correction: all references to "Pearl" should have been "Karma"

For everyday use, should i drain my Karma all the way before recharging or not?

If your regular/daily use pattern would normally result in rather small discharges (as a percentage of available battery capacity), then I would suggest going for a few days until the battery is mostly (more than half) way discharged, then fully recharging.

If your regular/daily use pattern is already using half or so of the battery capacity, then just recharge it each day.

Since the Karma uses Li-Ion (presumably with internal smart battery management), almost any discharge/charge pattern is tolerable.

The gain from optimizing your Karma power cycles is real (in terms of total battery lifespan), but I wouldn't go out of my way in this regard (and risk being without music because I miscalculated how much juice I had left).