# cycles from NiCad, NiMH, Lithium

[Joe Talmadge]

Hi,

I'd like to get a basic idea of how many times I'll be able to re-charge a well-made rechargeable battery. I have the vague (probably way too simplistic) notion that from NiCads I can expect something on the order of 1000 discharges before really seeing performance degradation, with NiMH it's more like 500, and with lithium (like my lithium cell phone battery) it's ???

Any info would be appreciated!

Joe

 

[zmoz]

All of them are about a thousand...by the time you wear them out there will be some new chemistry and you won't want them anymore anyway. /ubbthreads/images/graemlins/smile.gif

 

[lemlux]

The Li-Ion claims I've seen suggest 300 to 500 cycles.

The high discharge sub C NiMH claims I've seen go as low as 50 cycles. Non-R/C charge and discharge treatment will probably extend their lives significantly.

Regular NiMHs normally claim about 500 cycles and NiCads about 1000. In practice, modest charge rates and avoidance of overcharging probably makes the most difference in acheived lives.

 

[PeterB]

I've read, that LiIons have additionally a limited lifetime in the range of 3 years, independent of the number of cycles

 

[Lurker]

According to the reading I've done, it depends on the depth of the cycles, but your 1000/500 estimates for NiCd and NiMH are probably about right. The NiMH's will lose capacity gradually and NiCD more suddenly.

The life of Li+ is more closely related to absolute age than cycles. You should get 2 or 3 good years out of them and the more you use them in that time, the more cycles you will get.

 

[zmoz]

I'm allways worrying about the lithium batteries in my laptop, since they are so expensive...and I'm pretty sure they are rated at about 1000 cycles. Also I just bought 8 Lenmar 2000mAh AA's last night, said on the package good for 1000 charges.

 

[Ray_of_Light]

Li-ion are different from all other rechargeable batteries, since they rely upon a crystalline phase of lithium cobaltite. This material, if not used, produces a passivated layer that slowly brings the battery to death. This behavior leads to the misconception of the three years life, disregarding the use or non-use of the battery.
To avoid passivation of the cobaltite, that increases the internal resistance of the battery and diminishes the mass of active material, it is enough a cycle the battery every three months. In this state, you can store the battery until you reach the 500th cycle. The continue "standby" use or storage in a drawer will lead to battery death in about three years. Malfunction of the electronics built in the battery pack can only shorten battery life.

It is not bad, if you think that gel-cell (SLA) has a life of 200 - 300 cycles. SLA, anyway, stands better in standby/backup use, up to eight years.

NiCD are more resistant than NIMH, due to the intrinsic structure of negative pole, which is made of sinterized cadmium. They also stands better to overtemperature and overcharging. Also they may get to 1000 cycles. NICD usually fails due to defective sealing, that degrades the electrolyte, or because of a short circuit of the fiberglass separator , due to a growth of cadmium crystals in it. Both are pretty sudden failures.

Hi capacity NiMH (like 2100 mAh AAs) MAY cycle 500 times, if never allowed to overheat. In practical use, by driving heavy loads, they may actually overheat. Also, if not properly charged, they will also overheat.
These thermal stresses may ultimately lead to a life cycle of 50 times. NiMH stores hydrogen at the negative pole in a nickel-palladium "sponge", that is really sensitive to temperature higher than 30 - 40 °C. They dies usually because of the progressive degradation of the nickel-palladium sponge. KEEP THEM FRESH!

Hope it has been clear.

Anthony

 

[Lurker]

Thanks for the great information, Anthony. Can you please clarify your final advice to "KEEP THEM FRESH!" Does that mean to keep them away from heat, or to keep them fully charged? I don't quite understand what you mean by fresh.

Thanks.

 

[lemlux]

Anthony:

Interesting comments about the "use it or lose it" characteristics of Li-Ions.

Thanks.

 

[Ray_of_Light]

Sorry for the poor wording. My final recommendation is... keep NiMH as close as you can to 20 °C...

Anthony

 

[Lurker]

[ QUOTE ]
TheProphet said:
Sorry for the poor wording. My final recommendation is... keep NiMH as close as you can to 20 °C...

Anthony

[/ QUOTE ]
Thanks again, Anthony.
And for those of us who don't know (I had to look it up)... that's equal to 68 degrees Fahrenheit.

*********
Famous conversations in history...
Dr. Fahrenheit: "Sure is hot today!"
Dr. Celcius: "It's not that hot."

/ubbthreads/images/graemlins/grin.gif

 

[Joe Talmadge]

Thanks for the great replies, guys.

I've always had extraordinarily bad luck with rechargeable batteries, whether they were in my electric shaver, PDA, cell phone, whatever. By bad luck, I mean it seemed like the batteries often took half or less of the original charge in just a few months.

I've tried a few different strategies. A couple of years ago, I went on the assumption that I was having bad luck because "memory" was happening, even though the technical folks assured me that that wasn't the case. So I'd let the batteries run until they were completely discharged every time, then fully re-charge.

That didn't work, I supposed because by letting the batteries run down so far, I was always reverse-charging the deadest cells and killing them. Or maybe that's not the reason, who knows. Anyway, I then went on the theory that I should recharge the batteries after every use no matter what, regardless of how little used they were. Use something for a few seconds, back on charger, every time. My luck didn't change, I'm thinking now that if each little re-charging counts as a cycle, I could've just cycled out my NiMHs pretty fast.

I guess I'm going now with: don't recharge until at least 75% of battery is used, but don't run batteries into the ground. Recharge for a reasonable time then take batteries off charger. Maybe I'll have better luck, or maybe I'll swear off rechargeables forever. At this point, I definitely despise the technology.

 

[asdalton]

Running the rechargeable batteries until they're dead is probably the surest way to kill them. I used to do that, too, mainly because many manufacturers of rechargeable devices erroneously recommend it. Constant charging is bad, too. So your current strategy (charging after lots of use, but before the cells are dead) is good.

 

[Lurker]

If you discharge only 10% and then recharge, that doesn't count as a full cycle. It's just 1/10th of a cycle, so you could potentially get a lot more of these partial cycles than you could get of full cycles. Generally, NiMH batteries last longer with partial cycles than full cycles, so that is good. NiCD tolerate deep-cycling almost as well as partial cycling.

However, it is also important to fully cycle your batteries at least occasionally to keep their capacity up. This prevents crystal formation in the battery. Crystal formation simulates and is often confused with the memory effect. NiMH should be fully cycled down to 1.0 Volt per cell about once every three months. NiCD every month. Once the crystals have fully developed, reversing the process is not possible, or at least not practical without special equipment. Chargers with negative-pulse algorithms claim to prevent crystal formation without having to cycle the batteries.

Also, keeping your cells on constant trickle charge, such as many cordless phones or other household appliances are often used, is not the best for the cells. I think it is much better to charge the cells up and then take them off charge until they need to be recharged again. Whether that is a full cycle or a partial cycle doesn't matter, the point is that once fully charged, don't let them trickle-charge day after day-- take them off charge. Some people will put a trickle charger on a timer and trickle charge for a short time each day to keep cells at the ready without overdoing the trickle charge.

Also, no matter how well you maintain your batteries, they will give out eventually either due to cycle expiration or time expiration or accidental heat exposure. I don't see these kinds of batteries as long-term investments. Buy them and use them up.

I try to maintain a minimal inventory of rechargeable batteries so that they get used heavily, I charge them in a smart charger, cycle them occasionally and replace them when they need it every few years.

The real problem is when you have an appliance with a battery pack that cannot be replaced. This means that the whole appliance has to be discarded and replaced when the battery eventually gives out. I think manufacturers do this on purpose whenever they can get away with it as a way to guarantee product expiration and encourage repeat sales. You will get the most life out of these appliances if you follow the methods above.

Rechargeable batteries can be a big pain in the neck when they are not properly used and maintained, but can also be a big money-saver and convenience when used properly.

 

[Grummond]

Hey Anthony.

I found your post very interesting it answered a lot of questions for me.
I have copied your text into my PDA so I don’t loose the information. (I hope this is OK) I often come across a jewel of information here on CPF and then I forget and can’t find the thread, sometimes I can’t even remember the subject, I just remember that there was something interesting and I can’t recall what it was. Anyway thanks again, much appreciated. /ubbthreads/images/graemlins/thumbsup.gif

 

[batterystation]

All the above referenced information is correct and very well stated. The last thing that I might add that was not really mentioned would apply mostly to Li-Ion and NiMH technologies. That would be that the number of cycles refered to such as "500" for NiMH can be increased by a shallower depth of discharge. In other words, the Li-Ions and NiMH batteries will go more cycles if NOT completely discharged. Both like to be charged prior to "dead" and will give a little more service life if done this way.

 

[kitelights]

Great info. Clarification for some nagging questions that I've had for awhile.

Lurker, I haven't found a battery pack / appliance yet that I haven't been able to get into to replace rechargeable batteries when they go bad. Some of them aren't worth it, but I've always found a way to get to them.

I use the Dremel Mini Mites in my work and the replacement packs are $25 - $30. I can rebuild them for $4 - $6 with beefier cells than the original. You're right, they don't want you to know that you can open them up, but you can.