Is it ok to top off batteries as a normal practice (Li-ion, and NiMh)? I have the cheaper chargers (basically red-light/green-light stuff) . I may go a week or 2 of casual flashlight use, and then stick the batteries on a charger overnight for a top-off without checking the voltage.
Is this bad for the battery - shorten the run-time or lifespan? If you have a battery rated for 500 charging cycles, does the "top-off" count as a full cycle?
Thanks for any help.
Keeping your batteries topped off is good for them. The shallower the discharge, the more cycles they last. Just don't leave them in the charger once they're done charging, which for most cheap chargers, is bad for them.
--Bushytails
Everything you need to know about lithium-ion batteries: http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries
Topping off nimh-batteries is not the best way to keep full capacity. You do not have to discharge them completely every time, but you will have to discharge nimh's sometimes (till 0,9V, lower is not very good) before charging. How often depends on the type of nimh, a LSD does not need to be discharged every couple of months, once a year is enough.
For the best performance of nimh's you will need a good charger, i use the Maha MH-C 900.
I have a Maha-C9000. The verdict still seems to be out whether topping off batteries shortens their lifespan. I know the C9000 tops off for 2 hours, then goes into trickle mode. Both seem gentle enough rates. Some people take the batteries off right away when the main charge is finished, others let it 'top off'. I really don't enjoy babysitting the C9000 so I just leave the house or go to bed etc, and they are certainly topped off and trickled for many hours lol. I followed this procedure for 3+ years and so far the batters are still reading a healthy capacity when I use the 'Break-In' mode.
It's up to you whether you want to accept a slightly lower capacity while potentially gaining a longer lifespan, or get the absolute most juice into the batteries yet maybe lower the # of cycles.
Maybe someone here has links or some sort of experimental evidence to better answer this question.
Edit: I would doubt 'topping-off' counts as a full cycle. Perhaps a fraction towards your next cycle [charge /discharge]. Also, keep in mind even though batteries are rated for 500, 1000, 1500 cycles etc, this is likely under ideal lab conditions and will depend on how you use them and what device you charge / discharge / maintain them.
I think keeping the battery somewhere in the middle is the best for it over the long term and then partially charging it frequently to avoid deep discharges. This is what the Toyota Prius does with its NiMH battery pack. It tries to keep the charge in the middle, never going too low or too high.
For lithium-ion batteries it is best to store them around 3.8V at rest, so that seems to indicate they like to hang out at about that level. Charging frequently back to 4.2V is not good for them. With li-ion batteries, most chargers are going to trickle charge for a while so it seems like to me you could do what you are doing now, but only charge the batteries for 30-60 minutes instead of waiting for the light to go green at 90-120 minutes. That way you aren't fully charging them, but you are still putting most of the charge back in.
Nihm's - Every now and again a full cycle is good - maybe more than one ..
Li-ion , try and charge before 3.5v , I usually aim at 3.8v ..
The Li-ion drops off around 3.5v and if you consistently run them down past 3.5 you will shorten there life span ,
I know some cells say its ok to discharge to 2.75 or even 2.5 volts but I would not make that a habit , besides a lot of lights will go into protected mode once you hit 3v under load in anyway's , protecting the battery from over discharge .
Hmmm , that gives me an idea of something to write about :
I agree with that. Every now and then you need to clear the cobwebs out of the battery.
Thanks everyone. I guess I need to save up for a better charger.
A couple of observations about Li-on batteries and how to charge them.
1)Li-on are the most common batteries found in laptop computers and cell phones. Those two applications alone probably outnumber flashlight usage by a factor of something like 200,000 or so to 1.
2) Folks who use cell phones and laptops don't care if they drain their batteries totally. They also don't care if they top them off daily. I have been using a laptop as my work desktop since 1998, and always have it plugged into a power supply, 10 hours a day. I've gone through 4 laptops in that period, but I have only ever had one battery go so dead that I could not revive it.
3) Li-on batteries are now making their way into the high-end ($300) portable power tool market, as in battery-powered drills, etc. Huge draw, and guys who buy those things drain them until they won't run then pop another battery in.
4) I've left LI-On batteries in my cheap Chinese chargers overnight several times, and they always shut off at 4.2v and there has not been any problems with them.
So my take on them is treat them however you want. If they can power an drill until they die or your laptop everyday, or the gaziooilns of cell phones out there that get plugged in every night, they should do just fine in a flashlight, where for the most part they get much less frequent usage.
Li-on batteries scared the heck out of me when I first started the flashlight hobby (especially the cr123 batteries) but the more I realize how widespread their use is, the less I'm concerned about them.
+1
My DSD charger sometimes overcharges my Li-ions to the point of setting off protection, so I definitely would be careful with cheap chinese chargers and cells, if not for the safety reasons, than for the battery health reasons.
While it's true that li-ions are found in a lot of abused electronics and tools now, the protection and safety measures implimented, and probably the quality of cells and protection, are most definitely higher that with the stuff we use here. Should I mention quality control issues?
I don't want to read a thread about someone's house burning down or hand being scalded (oh wait, heard that one already).
I don't want to read a thread about someone's house burning down or hand being scalded (oh wait, heard that one already).
You're taking all the fun out of it.
Tools typically use the lower-capacity LiFePO4 cells or similar, which are much more resistant to abuse and much less prone to explode when abused, compared to the LiCo cells we use for flashlights.
--Bushytails
I'm curious about that; both Milwaukee's and Hitachi's sites just say they use Li-on cells, they do not specify which variant they use. My bet is Pansonic's or Sanyos, just like in a laptop., but that is just a guess.
lithium drill batteries I recovered cells from mostly had Samsung LiMn cells and one had Sony LiMn cells.
Dewalt is lithium iron phosphate, apparently with Sony or A123 cells depending on the model.
Milwaukee appears to use Samsung, but special cells designed for continuous 30A discharge from a 1.3Ah cell, unlike ours which are limited to 2C. I can't find what the chemistry is, but probably not standard.
Hitachi and Rigid seem to use Sanyo, again very high discharge rate cells.
--Bushytails
Wow, 30A discharge from 1.3Ah cell? That's 23C. There are lithium chemistries that can do that? What did these tools use before these were available?
Can someone get Match these cells so he can make something really crazy?
Before these, all power tools were nicd, with the exception of bosch's short-lived/failed attempt at nimh. And they are low capacity nicd cells too, due to using sintered instead of foam electrodes, for the lower internal resistance.
Most tools still are nicd - li-ion is only being used on high-end optional batteries. I can't think of any brand that uses li-ion as standard instead of an upgrade. Dewalt is pushing them, but they still cost double their nicd ones, which are still stock in most kits.
Nicds may not have the highest capacity, but they are good with high currents. I've pulled 50C before with no problems. And you can charge them in 15 minutes without significant degradation. Some nimh designs come close, but they don't match nicd, and the life of nimh tends to be a lot shorter when treated that way.
--Bushytails
Has anyone on this forum ever had a Li-on go *poof* on them? In reading the scare forum on CPF, seems like most of the accidents happened when the battery was in the light (not on a charger) and, interesting, most of the bad ones seemed to be when the light was not even turned on.
Additionaly, there seemed to be a lot more accidents with cr123's than with 18650, though that may change now that there are lights out there with multiple 18650's in them.
Reading some post seems that accidents are often connected with multiple battery flashlight. My opinion so far is that single battery and "standard" charger can't cause accident unless they are defective but maybe you can see there's something wrong before use them (for example checking voltage). If you need to use multiple battery, double check every time the batteries.