Numb battery question: How do you make a small battery pack

[jazclrint]

First off, these questions are directly for my bicycle light project which will be a 12.8V 3.3Ah 4s1p pack. I am looking to sort out the LSDs (Little ****ty Details) so that as I hopefully one day move on to a bigger project I'm not asking the same numb questions.

So here it is, how do you build a battery pack? Ok, so my old NiMH 5s2p pack has thin flat metal "bars" connecting them, then there was a paper cover over the ends, a bit of saran wrap, and then 2 layers of heat shrink, and maybe some sort of voltage/current protector in there (little white rectangular do-dad in series with the batteries. And the "bars" don't look to be soldered but tapped in in place with a fine point. I'd rather solder something for a greater contact surface. The batteries I am looking at using are basically long C cells (26650).

So what is the best way to connect my batteries? Do I buy or make these nice little flat bars, or is good old wire acceptable? If so, what gauge? I know there is a calculation for this, but I don't remember it. I can also get them with with tabs added for 25 cents a battery. Would that do? I can get those nice square plastic battery holders for these, just like the ones you can get for the headways. How do I wrap these up, or protect them from the elements? I have a nice case that will be sealed, but this light is for my MTB, so better safe then sorry. Also, what kind of voltage/current protector should I use to protect the LiFePo4 batteries? I will use a charger specifically for those, so I am not as concerned about charging as I am worried about excessive discharging from a wire shorting out or something. And, how do you balance batteries that are in series? More importantly, for a max of 18 watts worth of LED draw from LiFePo4 with a charger designed to work with a battery pack that size, do I really need to worry about it?

Also, does anyone know about the Battery space website? Do they sell good stuff?

A gentleman on the MTBR DIY light forum was helpful when choosing LiFePo4 batteries, but suggested I leave soldering a pack to the professionals. I replied, but it would have been better off sending him a resume. Someday I'll grow up. There is also quite a bit on the candlepower forum on bicycle lights. But I have yet to take the time to sign up to ask questions, and I saw nothing on building packs there, at least for bicycle lights.

Thanks,
Rich

[jazclrint]

Well, I've already figured out the protection part. The same site sells a little PCB with circuitry just for this very pack, for $9. So now I guess I'm going to need wire. Just have to figure out what gauge now.

[chef]

And the "bars" don't look to be soldered but tapped in in place with a fine point. I'd rather solder something for a greater contact surface. The batteries I am looking at using are basically long C cells (26650).

Those indentions are probably electric spot welds. Battery tabs often don't take solder. Can't remember what metal it is (aluminum?) but that might be a frustrating experiment.

Spot welders are expensive lil buggers, even the tiny ones. When I replaced a bad cell in a power tool's battery pack, I took it to Batteries Plus and they spot welded the replacement cell for free. I bought the cell from them and the welding service is complimentary with it.