When charging a Li-ion battery, how does the voltage of the charger affect the charge? My old Nokia cell phone came with a charger (an AC-to-DC adapter) which had a particular voltage. At one point, I bought a replacement charger, which was obviously not an exact replacement, because it was a different shape and had a different spec’d output voltage on it (it was an official Nokia part, however, not some 3rd party thing). I also noticed that there are “quick chargers” available, and I gather that they will charge a battery quickly, but “not as well,” whatever that means. Presumably, they have a different (higher?) voltage on the output as well.
So my questions are:
Is there something different about the charge given to a Li-ion battery with a high voltage source as opposed to a low voltage source?
Would this difference affect a battery’s useful life?
Is it a bad idea to use my old Nokia’s charger (3.7VDC) with my new Nokia phone (whose charger is 5.6VDC)? It would be nice to have one at home and one at work.
Assuming it’s not a bad idea to use either one, is it a bad idea to use both (e.g. alternating between the two)?
My last phone’s battery died a painful death, being useful for only a few minutes near the end. I’d hate to think I sped that along by my failure to adhere religiously to some battery charging regimen which dictated the exclusive use of the original factory charger.
However, given that my old phone and my new phone had chargers with different voltages, and yet Nokia sells a charger that has yet a 3rd voltage, but claims to work with both models, I find their dire warnings to only use specific chargers a little unconvincing. Am I right to think this way?
…and while I’m asking, how would all these questions apply to NiMH batteries?
It’s the current, not the voltage, that makes a difference in how quickly the batteries will be fully charged. The capacity of the battery will be given in milliampere-hours (mAh), probably somewhere on the battery. To find approximately how long it will take for the battery to be fully charged, divide their capacity in mAh by the charger’s output in mA to get a charge time in hours. If you’re charging more than one battery at once, divide the charger’s output by the number of batteries or add up the total capacity of all of the batteries.
About quick chargers: Lithium-ion batteries can be rapidly brought up to about 70% charge if the charger’s current is sufficient. That is, a ‘quick charger’ can give you a 70% or 80% charge in one hour. Bringing the batteries to 100% charge takes longer (see here). Quick chargers supply a higher current, not a higher voltage.
AFAIK, the only important thing about the voltage is that the charger’s voltage should match the battery’s voltage at full charge. (Although I have a charger that draws 12VDC for four AA cells; I’m not sure why.) If your new charger is 5.6 VDC, you shouldn’t use the 3.75VDC charger, as it may not fully charge the battery, or may take too long to charge it. (I’m not sure if this refers to the voltage supplied by the transformer block to the charger or that supplied by the charger to the batteries. The batteries themselves will also have a rated voltage – do you know what it is?)
Yes, it could. If the old charger can’t fully charge the battery, obviously the battery’s life per charge cycle will be shortened. Li-ion batteries are especially sensitive to heat, and it is very important that they are not overheated because permanent reduction of the battery’s capacity will occur.
3&4) I wouldn’t recommend it. The best case is that the old charger will be less efficient; the worst case is that you might damage the battery.
About your old battery and 3rd party chargers: If the manufacturer says one charger will work with different models, they’re right. The warning not to use third-party chargers can probably be safely ignored, though it might cause warranty problems, and you need to be sure to use a compatible charger (with the same voltage and similar current). An inappropriate charger could overheat the battery and irreversibly reduce its capacity.
About battery life for NiMH and Li-ion batteries: See here again. Li-ion batteries have high capacity and charge quickly, but they have some disadvantages (poor tolerance to heat, gradual reduction in capacity over time). Your old battery was probably either damaged by heat or simply deteriorated over time. There are ways to prolong the life of Li-ion batteries (listed on that site), such as frequently taking the battery through an entire charge-discharge cycle, storing the battery with certain levels of charge, and protecting it from heat. Still, a Li-ion battery cannot last more than a few years because of the chemical instability of that type of battery. The Battery University site also gives advice for NiMH batteries. Remember, though, neither of these battery types have the ‘memory effect’ that people feared so much in the old nickel-cadmium batteries.
So I just looked at my new battery, and it is marked “3.6V”, which would imply that the 3.7V charger from my old phone should be ok, right?
Also, I don’t quite understand your “battery capacity divided by current output of the charger” in order to get the charging time. Shouldn’t the voltage of the charger factor in there somehow? Also, that simplistic calculation doesn’t jive with the description of batteries coming up to 70-80% and then taking much longer to get up to 100%.
One additional question: I always hear recommendations to occasionally do a full discharge cycle (and the manual for my new phone said to go through three full-discharge-full-charge cycles when I first get it), but I don’t actually know a very good way to discharge the battery. I ended up waiting almost a week for the battery to get low, then playing one of the stupid built-in games until the battery died, since I wanted to charge it overnight and not worry about it dying in the middle of the next day. That’s a little bit of a nuisance. Is there a better way?
Ok, now that I look closer at those links you provided, I think Battery University is going to be able to answer all of my questions, and then a few that I didn’t have yet. Thanks for the links.
Thanks for the links.