Right, so after a new light.

Those Cree 3x XML T6s look nice but I reckon from past experience that the battery pack will be the weak element of the package and as such I want to make my own with decent quality batteries.

The standard battery pack is some sort of 4 x 18650 cell configuration but I can’t workout the set up to get the 8.4v it’s stated to be. Some sort of circuitry within the battery pack?

Best I can work out is; 2 pairs of 3.7v 2500mah cells in parallel (so 3.7v 5000mah) connected to each other in a series so giving a pack of 7.4v 5000mah. Would this work?

As is pretty apparent I know very little about electronics!

If someone could help or point me in a good direction of making a 4×18650 pack, that’d be grand.

Many thanks.

I have one of those lights, £20-odd from the bay. Its fantastic, used it for the first time last weekend.
As you say though, I’m concerned about the quality and longevity of the battery pack. I timed it indoors from fully charged to going off and it lasted just over 2 hours, which I was quite pleased with.
I did a wee bit reading up on these LED’s and I think they’re extremely tolerant of fluctuations in voltage, so maybe a 9v battery pack, or even a 12v might work with them. A lesser voltage could also work as well though.

You’re right about the battery pack, they may work, but are cheapest crappiest batterys they can put together. Sometimes they are even reclaimed laptop batterys!

Remember, a 18650 is 3.7v nominal and 4.2v fully charged, hence the 8.4v, so the way you said is what you need to make.
You will also need to add a protection circuit to them too.

Or, you could get a ready made pack from Smudge.

ps.
I wouldn’t recommend you try and solder Li-ion unless you really know what you’re doing. If you do it wrong or heat the battery up to much….well, an explosion may be on the cards!

battery packs are best left well alone, a new set from smudge, etc is cheaper than a new pair of hands/ eyes!

i recently dug out a ‘DX’ 4*18650 that had died on me. after removing the plastic outer i then tried to see what the problem was, figuring that i could at least salvage something.

the four batteries seemed to be well attached to each other and the top cap contained a surprising amount of circuitry.

trying to seperate each battery led to a puff of smoke emerging from the pack so i binned them asap.

like i said, best left to the pro’s. 😳

Lightmalls 10000mah
Is this the kind of thing you’re after?

As an alternative method if you have 4 18650’s and a charger already how about something like this….

http://www.batteryspace.com/battery-holder-li-ion-18650-battery-holder-2s2p-with-2.6-long-20awg.aspx

I have built several of my own lights and batteries in various configurations including soldering up 18650 li-ion directly or using cell holders like those suggested by mark90.

Each method has its own pros and cons but I would also agree with other posters that if you have very little soldering experience, not to try soldering your own pack.

I don’t know the light you are referring to but assume that you have got the size requirements correct i.e. 8,4V. What you need is usually referred to as 2S2P or two pairs of serially connected cell connected in parallel, as you rightly concluded.

It would be easier to create a DIY pack using something like one of the cell holders suggested above but that one is from a supplier in the US and you will probably find the postage prohibitively expensive. In addition it will still require some soldering of a suitable connector to the light and a charger as well.

All-in-all I think you would probably be better off contacting Smudge at mtb batteries and detailing your requirements and being guided by him. In the long run, by the time you have tooled up and bought all the bits, that will probably still work out as the best option.

I wanted by build my own but had difficulty in purchasing a protection circuit. Only one I could find was on eBay but they didn’t ship to the UK. I could have imported one from the US but they wanted silly money.

I just brought another DX T6 light, which cost less than £25.

afaik it’s not safe to charge or discharge LiIon batteries without some kind of circuit, like you could with NiMH ok. going too high or low kills them or blows them up. then you’ve got sealing and durability to worry about.

lots of MagicShine and other chinese lights use that voltage so just buy one of their waterproof packs for about £20?

afaik it’s not safe to charge or discharge LiIon batteries without some kind of circuit, like you could with NiMH ok. going too high or low kills them or blows them up. then you’ve got sealing and durability to worry about.

In general that may be true but in reality there are a lot of circumstances where this is not the case and there are a lot of scare stories about li-ion cells which to a certain extent are exagerated. I think a lot of those are also down to confusion between li-ion and lithium polymer cells which are a lot more volatile and hence dangerous.

For instance you can buy 18650 cells with an individual protection circuit on each cell which will protect each cell in a pack from over or under charging. I have successfully created several packs of varying configurations by just leaving the individual protection circuits on and (carefully) soldering the cells together so as not to destroy them.

I’m not saying this is an ideal solution but it is possible and amounts to the same thing as creating a pack using one of the multiple holders and charging and discharging them as a whole. I would always use a decent charger in this case as well, one that cuts off at the required voltage and doesn’t over charge the pack causing one or other cell to cut out.

If you have a light with a decent controller on board as well it will monitor the battery voltage and give some warning of low voltage at least before cutting out to prevent the battery pack from over-discharge. In that case you wouldn’t really require any sort of protection circuit to protect the battery other than maybe for peace of mind.