does anyone here ever build his own battery pack for bicycle light before?
i’m trying to build a bigger battery pack to be use for longer running time.
i bought these batteries from fasttech… i’m thinking using 8 of them together 
6*18650 Battery set For Bicycle lights/Bike light ( something like this)
my question is… how do you connect them together? can you solder them together?
i’m afraid the heat from the solder might spark a fire or something :~
any advise?
No. Just don't use those batteries, they have wildly different capacities and are complete shit. If you use them there is a decent chance of a vent with flame accident.
i’m going to use one of the wire from the older battery pack… it has somekind of protection for it…
when i cut open the old battery pack… 2 of them are 4.0V and the other is 2.6V
i got the feeling at least the one from fasttech is better than no name brand that came with the bicycle light
The one from Fasttech is as no name brand, you obviously do not know what you are doing so for your sake don't screw around with this.
For the last two months members here have unanimously been strongly encouraging you to avoid Ultrafire batteries, and telling you why and how they're dangerous. You don't seem to want to hear it, so I'll tell you what you can hear. Go ahead and get these Ultrafire batteries. They're a great bargain, and can't be that bad, and are most likely very VERY good, especially when you use in many of them in serial and parallel. You haven't had a problem yet, and that's not luck, that means you never ever will have a problem. Others will perceive my last three sentences as sarcasm, and they'd be correct.
Where would this battery pack go? In a jersey pocket along your spinal cord? Hanging off the handlebar just below your face? Or hanging off the top tube between your legs and near your family jewels?
I'll second leaftye here, just place it right near them while charging.
lol…i appreciate the sarcasms and the concern…
but i’m planning to reuse this protection that came with the older battery pack…
i just tested all the batteries in that pack… two of them are 4.0V and the other 2 are 2.6V…
it seems like the protection kicks in( shut down) when the battery fall below the set limit (2.6?)
my only worry is about soldering them together…
they seems like their being “tacked” instead soldered
Daylighter, let me put it in simple terms.
Protection no prevent boom boom!
is it better if i used protected batteries instead?
something like these protected sanyos batteries ?
What is important is well matched name brand batteries, as you do not have the ability to weld tabs onto the batteries you need some with tabs already on them. I already put in a request for some.
where did you requested from? 
I have built packs with the red and black flame trustfires and I can tell you scaru is trying to help prevent long term failures and keep you safe. If one battery in your pack is not up to par the whole pack is bad. Laptops most of the time only have one battery that fails and the pcb will refuse to charge the pack leaving it unuseable. You will be much better off spending a little more on the batteries getting something of quality like a Samsung or Panasonic 2600mah that will last years. Tabs will also make the building of the pack much easier.
You can also find pcb for packs at batteryspace. I purchased mine off ebay from some china seller cheaper. same pcb as what battery space was selling.
Those are spot welds. I wouldn’t recommend soldering to li-ion batteries unless you are quite proficient with soldering. Li-ion batteries are very sensitive to heat and are very easy to wreck even if you leave the iron on it for a little more than necessary to form a solid soldering joint.
I’m not saying it can’t be done, but there are easier ways like getting a 18650 battery holder (example )
how did you built your battery pack? did you soldered them together? did you use protection circuit?
edit: thanks for the link… i was thinking reusing the PCB that came with the old battery pack
It can be done but you will need a soldering gun not a iron. A gun with a 100watts or better. You need enough heat to get the solder flowing quickly there’s a lot of mass your heating. I wrapped the battery with a wet towel while soldering and as soon as the joint was soldered a stuck the wet towel to the joint keeping the battery from absorbing to much heat.
I would not really advise anyone to do this it could go boom. But its your choice just like it was mine. When I build another pack I will purchase batteries with tabs. Much safer.
One more thing I forgot to mention. If you have the space the battery packs from hobbyking are the cheapest easiest route. Pick your number of series cells you need for voltage and pick your mah’s you need. I didn’t have the space but I figure on a bike you could make it work. They also already have the balancing wires for hobby chargers wired in.
Fasttech, I'll tell you when they reply.
hmm… do you think this Lipo battery last longer than the original battery pack that came with light?
do you think batteries like these will work? it has tabs on them… i was thinking just soldering between tabs?
and add the original PCB protection board that came with the old battery pack
Daylighter, as I have said time and time again: Those batteries are complete crap!