+1000! 
No offense mate,
But if you're going to ask for advice on a topic, then go on to ignore it, even from well known and respected guys on this forum like scaru, then you might as well not ask it.
Batteries may seem like a commonplace and harmless item, but their potential for harm is extraordinary, especially from relatively new tech like Li-Ion batteries which are known to release toxic chemicals even when just opened, let alone if something goes seriously wrong and they explode, which may seem a rarity, but you're playing with DODGY batteries which may have god-knows-what.
I understand that you might wanna save a few bucks, because it can get real expensive, but it's really not worth serious burns, acid burns, fume inhalation, blindness or any kind of injury.
If you really want a massive battery pack, go get KINGKONG 26650's. Even just 2 of those will beat the crap out of more than half a dozen ____Fires. Heck, go D-sized 32600s.
hmm…32600s? it’s nice… but it’s a bitching recharging them for more than 17 hrs ( it took almost that long to charge “10000” mAh 4 26650s battery pack the one that i got from lightmalls :laughing:
i wonder does anyone here know somebody personally that ever get injured due to the battery exploded?
except that poor old man i read somewhere in the forum ,somehow the CHARGER exploded…
i have few of them cheap batteries that quit on me while inside the flashlight… the flashlight just simply turn off.
the PCB kicks in and shut the light down… no poof, no smoke, no big bang… nothing…
the charger? same thing… it just simply won’t charge…
unless you do something really stupid with the battery… like put it in the oven or microwave them, or puncture it.
i hardly ever worry about it will explode on me.
all the bicycle battery pack usually have a built in PCB board on them… just today… 1 of mine decide to go dead.
i cut the plastic open… took some measurement on the battery… it turn out 2 of them has 4.0V and the other 2 was 2.6V
again… the PCB kicks in and shut the pack down…no poof … no smoke…nothing
just like driving a car… it’s only scary when you do stupid things to it 
Dayighter, there has been atleast one person on here (off the top of my head) who has had a battery explode and on CPF there are many more. One of them was actually hospitalized and had permanent lung damage.
Cruising down a highway at 120km/h (or 70mph), would you rather be in a car that you don't know how it was made or whether the brakes work properly, it has an adequate crumple zone and it even has airbags installed, or would you rather be in a car that's gone through rigorous safety testing with a 5-star ANCAP rating and so on?
Sh*t happens to good drivers too.
Daylighter we are trying to save you some grief from or on experiences. While the cheap batteries might work they will not work correctly for long. The pack I built (against what I recommended my friend he choose because of price) was a 2s5p 10 trustfires with a balancing wire wired in with a 7.4v PCB. They will not balance out between sides. I had to make a special connector so that I could tap in each side to charge the two paralleled sides individually. This was a friend of mines hunting light. He has returned twice saying that the hobby charger refuses to charge the pack. I have to use the adapter I made to get the cells balanced again. One side of the packs paralleled cells is almost dead while the other side is almost fully charged. So when the charger see’s the fully charged side it terminates the charge. Then he can’t charge the pack I have to do it individually. Pain in the * considering that’s almost 12,000mah at 4.2v on one side. Takes awhile to get charged up. No matter how slow I charge the pack one side’s voltage always measures less than the other. I would assume that one side has a cell or cells that is not quite up to par. It causes that side to lose voltage after it sets for awhile, Bad cell high internal resistance. This cause the pack to have less capacity on that side when drained and the other side still has capacity remaining. Then when charged it never reaches full capacity again because the other side trips the charger when full. Leaving the weak side only partially charged. And the cycle goes on and on until there completely out of balance. He is considering getting me to rebuild the pack with quality cells. And I recommended it for safety, reliability and no more charging problems.
A quality cell while it may cost more will save you time and money in the long run no matter how you want to look at it.
i threw this together quick just to get commentary going on the right way to do it. please pick it apart.
fire away. i know its not completely packaged up nice but….
Kevin, when using li-ions in series it is recommended that you balance charge them rather than bulk charge.
in this application i would charge cells separately in xtar or nitecore charger then install in battery pack. good? bad?
^^^^Good.
13,600?
In series your voltage adds up for the number of cells 4.2vx4= 16.8v and your mah’s stays the same as one cell (3400mah). In parallel the voltage stays the same 4.2v as a single cell and the capacity (mah) adds up (13600mah). In parallel the batteries act as though it is one big li-ion at 4.2v with what ever capacity the total amount of cells give you. In parallel they can also be charged with out a balancing wire. The charge rate can also be increased because the current is dividing between the cells. So if you charge the paralleled cells at a rate of .5C (.5c x 13600mah) that’s a rate of 6.8amps. Just make sure when putting cells in parallel that all the cells measure close in voltage before you connect them together.
my pack is 2S2P 8.4v. so 6800mAh?
Correct. The charge rate can be doubled over what a single cell would be.
thank you. me personally, i am not interested in charging it as a pack. i will just charge them seperately in a quality charger. otherwise i think it would be prudent to build a pack with balance charging leads and use a hobby charger to charge multi cell pack. any thoughts on the safety of my set-up.
Shoud be good to go. I would mark these cells and keep them together as a pack. So that they will tend to see the same usage. Just remember their individual voltages needs to be close to the same before installing them in the holder. Panasonics are known to be good quality cells.
thank you. my charger hits 4.18-4.19 everytime. so far.
cool… i think i like that idea… it’s easier to build and monitor the batteries
now what if… i want it for longer period, can i link 2 of those together?
i think i can get some “cheap” protected sanyos from fasttech 
i think it would be possible to attach two of those battery carriers back to back to create a very large capacity pack. just be careful on your wiring. don’t want to short circuit anything. anchoring the power cord to the battery holder would be a good idea too. handling the battery pack could weaken the wires where they are attached to the pack. some other ideas: a velcro strap to hold batteries in the carrier, cover all wire connections so no short circuits, use trail tech or magicshine connectors (heavier wire and more positive connection). the carrier i pictured was not a plug and play unit. started as a 4S1P holder and was modified to its present state. careful attention to wiring and distance between posts(see solder blobs on terminals)to adjust distance for keepower 3400 18650 batts.