Hi there,
I am trying to figure out the best system to use lights. Due to cost, I'll most likely be getting NiMH batteries and from what I know these work best when discharged almost fully before recharging fully (but not overcharged). I also know that a lot of these lights are designed to be cooled by air passing over them while on a moving bike.

So, the question what is the best system to use and discharge the lights?

Most of the ones I am looking at have a battery life of about 2 hours and my ride would be shorter than this. However, when finished a ride I would have to discharge the battery for optimal battery life (right?) but I can't just leave the light on a bench somewhere on becuase there is no airflow and it could overheat. I also don't want to keep using it on the bike and possibly be stuck with no light when the battery runs out.

The best option would be the just recharge them when I finish the ride, but I am worried about effecting long term battery life by doing this.

So, if anyone here has any advice, please feel free to chime in.

Thanks in advance.

Nicad's are the batteries you have to discharge. With a Nimh setup charge them at will.

I would find out exactly how long they would power your lights at first though and maximize usage on them. If they'll go 2 hours and your ride is 45 minutes, I'd charge them every other day. Nimh batteries don't have a memory but I think they do have a limited number of recharge cycles (something like 8000 usually) so I wouldn't necessarily charge them any more than necessary, but I wouldn't worry so much about the state of charge when I did charge them.

I have a LaCrosse battery charger/discharger/refresher. Basically it's a computer for batteries, complete with LCD display for each cell, lets you charge, discharge and refresh cells at different currents, etc. I found out about it at candlepowerforums, go there now for more info on different charger/discharger units and battery info in general.

http://www.nimhbattery.com/la-crosse-products/bc-900-battery-charger-bc900/la_crosse_bc-900-nlg.jpg
Just a warning about NiMH batteries - at least with 2500 mah batteries, and this is my own experience with 2500 mah batteries. Just buy enough batteries to get the job done. NiMH batteries that sit on the shelf for a long time (self-discharging over a year in my case) will be completely dead and will not hold a charge when you try to recharge them again. This only applies to 2500 mah and up.

I learned this the hard way. I bought 50 AA NiMH 2500 mah cells (PowerEx, Panasonic, Energizer) for custom made battery packs. I used them all daily with LaCrosse chargers. The batteries worked to spec during the time I used them, then when my project was done I stored the batteries away. A year later, I bought a wall clock and took one of the batteries out and charged it. 2 hours later the wall clock stopped working. I charged it and refreshed it again and again only 2 hours of juice in the wall clock. So it was with the whole batch.

Even after weeks of cycles of discharging/refreshing/charging (someone at powercandleforums said they cycled a cell 50 times to revive it) I could not revive ONE of them. So if you do not plan to use the batteries, you must not put them away and forget about them. You have to refresh them every 6 mos. or so (just throwing that number as an example). Otherwise they will completely self-discharge and die like mine did. And btw NimH batteries self discharge much faster than NiCad.

HOWEVER, this only applies to 2500+ mah, because I also have a batch of older 1800-2300 mah NiMH AA cells that have been sitting on the shelf for even longer than a year and these still work. And after some reading on the candlepowerforums I see that I'm not the only one lamenting their mass die off of 2500 mah batteries.

Wow, i just realized i gave you way too much info without answering the question. Sorry.

Anyways like ovrrdrive said, you don't need to discharge as frequently with NiMH cells and I'd recommend discharging/refreshing with a unit like the LaCrosse which is designed to do this without damaging the battery rather than simply letting it drain to nothing.

Another opiton is to get some low-self discharge batteries like the Sanyo Eneloops. They are 2000mAh right now (I think 2100mAh but I could be wrong) and according to Sanyos spec retain about 85% charge after 1yr in storage. At 6months you still have about 90% charge as per Sanyo's specs.

Tot he best of my knowledge from what I've read on thr web from many sources all batteries can develop 'memory'. It is just that some battery chemistries are more prone to memory development as the cells age. From all I have read you should not always fully discharge NIMH cells all the time. A full discharge and recharge cycle every 10 recharges is from what I have read online as a good number to go by to keep the cells going strong. With NICAD's you can give them a full discharge every time or every 2-3 charges.

Also check out on Google 'Steves Digicam' and look in the forums. There is extensive research done on the Maha C9000 and Lacrosse BC-900. Look under the 'Batteries' area in the forums. Being photographers and camera people they are very critical on the cells and have a lot of feedback on the cells and how they operate in many enviroments that a photographer/camera person will be in. After all they depend on thier gear to be good condition and juiced up for that 'moment/shot' which they have to be at the ready aways.

Hope that helps. I have not tried this myself but from what I have read on the forums by keeping the cells in the fridge you can decrease the rate of the self discharge.

Nicad's are the batteries you have to discharge. With a Nimh setup charge them at will.

I would find out exactly how long they would power your lights at first though and maximize usage on them. If they'll go 2 hours and your ride is 45 minutes, I'd charge them every other day. Nimh batteries don't have a memory but I think they do have a limited number of recharge cycles (something like 8000 usually) so I wouldn't necessarily charge them any more than necessary, but I wouldn't worry so much about the state of charge when I did charge them.

First, you are off by a factor of about 10 on the number of recharge cycles for a NiMH battery. Their life is more like 800 cycles.

Second, they will develop a memory but they aren't a prone to it as NiCd. This has come up in other posts. You just need to do the discharge cycle much less frequently...like every 3 months or so. I do it more frequently than that (monthly) because it's easier to remember.

The best way to discharge them is to use a battery analyzer. The analyzer will discharge the battery to a 1.0V per cell in a controlled manner and then recharge the pack from there. Maha C777 Plus II (http://www.thomasdistributing.com/mh-c777plus.htm) is a good one but it is kind of expensive. On the plus side, it will charge just about any battery you care to throw at it.

Battery Space sells some (http://www.batteryspace.com/index.asp?PageAction=VIEWCATS&Category=838) too. I haven't use them so I can't say if they do a good job or not. They are slightly cheaper then the Maha but they don't look as versatile.

Don't discharge the batteries, just used them like you normally would. Just don't get into the habit of only using 10% of the charge before recharging, that's how you get in trouble. Other than that just use them and you'll be fine.

Don't discharge the batteries, just used them like you normally would. Just don't get into the habit of only using 10% of the charge before recharging, that's how you get in trouble. Other than that just use them and you'll be fine.

+1

It may not be the scientific method, but I've been doing it that way for years and have always been fine.

Most battery experts (I am not one) state that the memory effect does not exist with modern NiCds, and certainly not with NiMHs. There is no need to discharge them routinely.

It is damaging to discharge a battery pack consisting of two or more cells completely. One should not discharge them below about 1.0 volt per cell. Some of the cells will be forced into a reversed state, which, done repeatedly, will kill them.

Most battery experts (I am not one) state that the memory effect does not exist with modern NiCds, and certainly not with NiMHs. There is no need to discharge them routinely.

It is damaging to discharge a battery pack consisting of two or more cells completely. One should not discharge them below about 1.0 volt per cell. Some of the cells will be forced into a reversed state, which, done repeatedly, will kill them.

The Battery Bible states otherwise (http://www.buchmann.ca/Article10-page2.asp). The Ni chemistry batteries can recrystallize which shortens their capacity. NiMH just does it to a lesser extent.

Your other statement is correct. If you do discharge them 'completely', it has to be in a controlled manner and not below 1 V per cell.

Here is an excellent reference on NiCd and NiMH batteries. The author is highly qualified and highly regarded. To my knowledge he has no hidden commercial interests. I'm not sure the same can be said for the battery 'Bible".

www.rcbatteryclinic.com (http://www.rcbatteryclinic.com)

Here is an excellent reference on NiCd and NiMH batteries. The author is highly qualified and highly regarded. To my knowledge he has no hidden commercial interests. I'm not sure the same can be said for the battery 'Bible".

www.rcbatteryclinic.com (http://www.rcbatteryclinic.com)

Interestingly, he directs you to the Cadex Battery University. The Battery Book that I cited is written by Isidor Buchmann who is the president of Cadex Electronic. It is probably the best source of information on rechargeable batteries you can find. Yes, Cadex sells battery chargers and analyzers and test systems but that doesn't invalidate the information in the Battery Book.

Yes, but Cadex is the only reference I am aware of that recommends routine cycling of batteries. Others references either say cycling is not necessary or deny that memory effect even exists.

My personal experience, having cycled about 8 different NiCd packs many times each, is that cycling has never increased capacity. I cycle only to gauge battery health. A pack failure could destroy a costly model aircraft (my other hobby).

Sorry to drag out the discussion. My concern was people who read this thread will go out and spend money on cyclers. I believe that most NiCd and NiMH lifespan problems result from bad charging technique or from draining packs too far.

I'll shut up now.

Upon stumbling upon this thread, I remembered the 3 2500 mAH AA cells I had that were bought more than two years ago. They've been sitting in a box unused. I tried to charge them with my slow smart charger, and lo and behold, they quit charging in a few minutes. Tried it again this morning, same thing. They did power a flashlight, but I knew they couldn't already be fullly charged after sitting idle for so long. I thought they might be toast. But the neat thing is that after sticking them into my dumb charger and letting it charge for around 6 hrs, they work! I even tested them by having them run a 2 cell flashlight for 45 min straight with no dimming to prove that they've been successfully charged.

Moral of the story? If a cell that's been idle for a long time seems dead, sometimes hooking it to a dumb charger can yank it out of its stupor.

Upon stumbling upon this thread, I remembered the 3 2500 mAH AA cells I had that were bought more than two years ago. They've been sitting in a box unused. I tried to charge them with my slow smart charger, and lo and behold, they quit charging in a few minutes. Tried it again this morning, same thing. They did power a flashlight, but I knew they couldn't already be fullly charged after sitting idle for so long. I thought they might be toast. But the neat thing is that after sticking them into my dumb charger and letting it charge for around 6 hrs, they work! I even tested them by having them run a 2 cell flashlight for 45 min straight with no dimming to prove that they've been successfully charged.

Moral of the story? If a cell that's been idle for a long time seems dead, sometimes hooking it to a dumb charger can yank it out of its stupor.

It's not necessarily the charger. Ni chemistry batteries often need a few cycles after storage to get back up to full charge. Think of it as blowing the cobwebs out;)

Yes, but Cadex is the only reference I am aware of that recommends routine cycling of batteries. Others references either say cycling is not necessary or deny that memory effect even exists.

Buchmann's book is the only place I've run across that has a detailed, well researched and well presented explanation of what the memory effect is...and isn't. The formation of larger crystallites that caused a decrease in the capacity of NiCd isn't as pronounced in NiMH but it is still there...along with a number of other issues that need to be understood and addressed to insure the longest battery life possible. He states quite clearly that NiMH cycling should be kept to a minimum and suggest about a 3 month period between cycles. During the summer, I ere on the side of caution with 1 month cycling because I can remember to do it easier that way...which I have state previously.


My personal experience, having cycled about 8 different NiCd packs many times each, is that cycling has never increased capacity. I cycle only to gauge battery health. A pack failure could destroy a costly model aircraft (my other hobby).

Cycling the battery isn't about increasing capacity. It's about maintaining capacity. Chemistry and physics dictate that you can't gain capacity by any treatment short of rebuilding the battery with fresh electrolytes. As with any battery, what you had at day 1 is the best you can have! Okay, the best you can have is probably close to charge 3 or 4 on a Ni chemistry battery.;)

As for pack failure on a bicycle light system, there is far more at stake than a costly model aircraft if the pack fails.

Sorry to drag out the discussion. My concern was people who read this thread will go out and spend money on cyclers. I believe that most NiCd and NiMH lifespan problems result from bad charging technique or from draining packs too far.

I'll shut up now.

The issue with cycling rechargers is that they are often the best way to charge the batteries. The fact that they can cycle the pack is a bonus. I have 3 Maha C777 Plus II chargers. They have dV and dT cutoffs to ensure that I don't overcharge...or more importantly with NiMH...overheat my packs. Most of the chargers that are shipped with commercial units are useful only as paperweights. Yes, the Maha's are expensive but so are batteries.