Hi,
i want to make my own battery charger. i already read few posts about charging Li battery and it's quiet complicated.
but the battery im using already have its own over charge/discharge protection circuit.
from what i know, i just need to supply steady 3.7 volt for it to charge. is it right? i'm new with lithium battery.
this is the battery.
http://www.ebay.com.my/itm/280966269159?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649
please free to drop any idea to me. thanks for reading 
Think you'll find all you need here : Complete Guide to Lithium Polymer Batteries and LiPo Failure Reports - RC Groups
From your specified link it appears the batteries you are interested in are 4.2 volts, so there's no possibility that 3.7volts will charge them.
I would recommend that until the OP is Very familiar with Li-Po batteries a professionally manufactured charger be used. A Li-Po battery is a Very Dangerous Device if improperly handled and although most cells have over/under voltage protection there is no short circuit or over current protection internal to the battery. If Shorted a Li-Po battery is a severe fire hazard, as is pointed out in the rcgroups.com thread. This is a website that has Extensive data and information on recharging Li-Po batteries. I found a lot of good information there.
Bob
Li-po chargers have a series of phases they go through as they charge a connected Li cell. In a rather simplified manner it goes something like this, generally they first read the battery cell voltage to determine that one exists and needs charging. Then it applies a constant current while at the same time monitoring the slowly raising cell voltage. At about 4.0v (per cell) it switches to a constant voltage output until the charge is completed at a nominal 4.2vdc terminal voltage.
Lefty
I'm gonna jump in here with the other guys, and recommend buying an off-the-shelf charger,
due to the problem that lithium batteries need special treatment during charging. Note the
pictures here,
Things are a little better now with the newer batteries, but this should be your starting point
into the world of lithium.
UltraFire 18650
Before you invest all the money / efforts to figure out a charger for it, you may want to crack open one of those batteries. What's inside may surprise you.
Docedison:
I would recommend that until the OP is Very familiar with Li-Po batteries a professionally manufactured charger be used.
These are LI-Ion batteries, not Li-PO.
A Li-Po battery is a Very Dangerous Device if improperly handled and although most cells have over/under voltage protection there is no short circuit or over current protection internal to the battery. If Shorted a Li-Po battery is a severe fire hazard, as is pointed out in the rcgroups.com thread. This is a website that has Extensive data and information on recharging Li-Po batteries. I found a lot of good information there.
Bob
Agreed, but again, these are Li-Ion batteries. Li-Ion batteries are MUCH safer than Li-Po batteries, otherwise they wouldn't be in every mobile phone. I've never heard of a mobile phone bursting into flames...have you?
Henry_Best:
Docedison:
I would recommend that until the OP is Very familiar with Li-Po batteries a professionally manufactured charger be used.These are LI-Ion batteries, not Li-PO.
A Li-Po battery is a Very Dangerous Device if improperly handled and although most cells have over/under voltage protection there is no short circuit or over current protection internal to the battery. If Shorted a Li-Po battery is a severe fire hazard, as is pointed out in the rcgroups.com thread. This is a website that has Extensive data and information on recharging Li-Po batteries. I found a lot of good information there.
Bob
Agreed, but again, these are Li-Ion batteries. Li-Ion batteries are MUCH safer than Li-Po batteries, otherwise they wouldn't be in every mobile phone. I've never heard of a mobile phone bursting into flames...have you?
Li-ion battery cells still use the same charging requirement, start with constant current until near end of charge voltage and then switch to constant voltage to reach end of charge voltage. Li-po tend to be more dangerous because of their higher current discharge capability compared to Li-Ion.
Henry_Best:
Agreed, but again, these are Li-Ion batteries. Li-Ion batteries are MUCH safer than Li-Po batteries, otherwise they wouldn't be in every mobile phone. I've never heard of a mobile phone bursting into flames...have you?
No, the basic Li-Ion chemistry is not much safer. There have been cases of phones overheating, and also laptop batteries. I thought the HP problems were well known. Sony too, IIRC. And, in the world of electronic cigarettes, the problem with Li-Ion batteries is well known too. Battery University is a great resource. I suggest people read there. Candlepower Forums as well.
There are some Li-Ion family battery chemistries which are much safer. Lithium-Manganese, and Lithium-Ferro-Phosphate, for example.
The Li-Poly designation has nothing to do with battery chemistry.
Lithium polymer battery - Wikipedia
The primary difference is that the lithium-salt electrolyte is not held in an organic solvent but in a solid polymer composite such as polyethylene oxide or polyacrylonitrile.
The wikipedia article further mentions that the positive electrode is either Lithium Cobalt or Lithium Manganese. Of these 2, the Cobalt salt is the common Li-Ion material, and so any Li-Poly battery using such chemistry will not be inherently more or less safe than other common Li-Ion cells. There's a reason why you can find 'protected' Li-Ion batteries. The manufacturers of these (AW, Tenergy, Ultrafire, etc.) add the protection circuit to the cell. But these protection circuits can fail too. In a mobile phone, the battery is a Li-Ion, even if it's a Li-Poly configuration. The overcharge protection circuit is included in the phone's electronics. The protection circuit should also protect against over discharge, both in terms of excessive discharge, and overcurrent.
I don't use common Li-Ion cells at all (except in my phone, where I have no choice, and in fact I don't know specifically what chemistry it uses); I use LiMn, and will probably be using LiFePo in the future. I also use a Pila IBC charger. Lots of people (this is from the e-cig forums, and flashlight forums) don't trust the cheaper chargers to shut off. (Similar to a couple recent threads we've had here on el-cheapo DC-DC converters.)
Also, as I understand it, lithium fires can't be extinguished with water. So buy a good charger. If you want to be really, paranoid, there are Li-Ion charging bags.
(Found that at Super-T manufacturing, who is targeted to the e-cigarette market.)
I Stand... Wow, Thank you for a really great and Highly "Bookmark-able" Post. You have managed to clear a lot of my doubts and questions up.
Bob
You're welcome. Glad to find something I could speak to.
BTW, I can think of cases where I might find it reasonable to build a battery charging circuit. A remote device, where batteries are used as an energy store, and charged with solar. Even there, I'd look for an IC purpose-built for the battery type. But the OP didn't indicate any such installation.
So for fun I followed that e-bay link. The seller is advertising those batteries as 'safe and environmentally friendly'. Hah! Well, the protected batteries are pretty safe, but lithium salts aren't 'friendly' at all, AFAIK. Just FYI, I've had the switch / regulator / protection circuit on 2 e-cigs fail in the dead-short mode. Didn't smell as bad as burning plastic, and I caught it before it did any damage.