Li-Ion Pack ?'s for Headlight Project

I have just stumbled on this site a week ago while doing research for building a LED headlight and have probably logged over 40 hours this week alone looking at all the posts! I have learned a lot but there are a couple of questions I had about the battery pack I will be using. I was planning on using 14.8v pack with 4 18650's in series. I wanted to be able to use the charger to power the headlight as well, in case I forget to charge it ahead of time. I am guessing that I would need a pack with 2 outs for the charging and discharging? If that is the case, i have found lithium polymer packs that have this feature but have not been able to find any Li-Ion packs that have this....... They just have the one out. Is there a way to add one more out to a li-ion pack? Or if I am asking a completely stupid question (forgive me) and if someone could lead me in the right direction that would be great or even give me some resources where i could learn more about this......

Thanks for the help!!

I do not understand! How You are planing to use charger to power the headlight? I do not see any sense to use headlight powered in that way. Lithium poylimer packs commonly have balancing tabs, and there is not reason against to use them with LiIon packs, I think.
Anyway, I think that you can cheat "smart" charger and power the Led - you can use LiFe, LiIon or Lipo x number of cells as option for voltage, and current as you need, but it have to be connect with main output of charger, not balancing tabs. Some balancing chargers will not charge battery without balancing tabs. Some charge exclusively through balancing tabs.

have you seen the new charge management boards?
http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=4888

i havent tried one yet , helps if they are in stock but its interesting.

many 14.4 li-ion packs are made with "Pack protection" which keeps any single cell from discharging to low, overcharging, and also has a input output amperage limitations to keep shorts and wrong charge rates from hitting the cells. protection is good and it makes the pack safe and Useable.
but unfortunatly these protections are not "balancing" so the pack stays within specs for each of the cells, and for quite a few charges it stays fine, but without balancing it eventually falls out of perfect, and looses capacity unnessisarily VIA the batteries being at diffferent levels of charge.
if you get a pack with balancing "taps" which is just wires off the cells, and a charger with balancing tap connections and all the "pack" will have each cell fully charged , balanced, and the longevity on the PACK will go up a large ammount.
A person could also do things cheaply, like using multiples of cheap chargers (insuring there is no problems from the the interconnections) and simple pack protection, or use Single Protected cells, with a holder and seperate to balance.

again most of the stuff you can buy out there, is crap, after your "warrenty" runs out the cells will be all imbalanced and the pack will suck, good enough for Christmas gifts and all you know 5 minutes of thrill was all that is needed anyways.
But they WILL do the job for about a good year at least.
a fully balanced properly charged pack with selective quality cells , could last you more like 5+ years, but you know by then you might have a new light design its all up to you, but i think that is some of what you need/ want to know.

Thanks a ton for the info.... I will now have to see if it will be worth it too balance the packs or not. It might be better not to because then it will give me an excuse just to design a new light when performance starts to deteriorate Part of my question was not too clear though and I will try to restate it........ (Noob Alert) I understand how it would work great if I just connected my pack to the charger, charged it and then connected it to my light but how would I go about putting a battery pack in a case and having one connector coming out of the case for the light and then one more connector coming out that the charger would connect to. I also wanted to be able to use the light while the charger was connected.... So i could use it and charge at the sametime (kinda like a laptop). I was wondering how to do this being that there is only 1 (2 cond) wire coming from the li-ion pack....... I hope that made it a little clearer

y adapter
there will be no more "voltage" on the battery (fully charged) than when on the charger itself, assuming it is a proper li-ion charger, so potenitally you can have the charge on and the light without any issues. any of the pack makers would gladly toss on a second connection for a mere few bucks more.
and make Sure that the pack is at LEAST protected, because it will be total junk in a way less time if you get some crappy unprotected pack.

if the battery has taps for the seperate cells, you can still use the 2 "end" ones to connect up to a load.

there would be very few chargers that would not be able to handle the load of the light working WHILE its charging, but that would also be a concideration, if your drawing 3amps off the pack and trying to charge it with a 1amp charger too, most the time it would not be a problem, but rarely it could be.

Thanks, that was what I was wondering. I appreciate the information and help

dontshoot80 said:

Thanks a ton for the info.... I will now have to see if it will be worth it too balance the packs or not.

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Please don't even think twice about this - virtually all Li packs need to be balanced or they become unstable.

As far as 18650s, if you buy cells that are completely individually protected and charge them in an off line charger, then it sometimes is easier.