Start with 1 then you can upgrade later if you want is my advice that’s what I did.
In the green graphine
4 ah is only just working
5 or 6ah are fine for DIY
Then it’s any thing up to 15ah (by the 3rd pack I was having to take brakes to stop thing getting to warm so I added a 2nd batty in parallel)
(higher better)
Over 15ah and you start risking exceeding the welder limits
I’m building a 12S8P 40T.
Alright.
Left on the list.
0.15mm by nickel roll( I’ll dig in the forum or maybe you have something in hand)
kaptontape
Fishpaper rings and sheets.
@moon suggested, been using them since in uk and I go for the 0.2mm
https://www.ebay.co.uk/sch/metal-mass/m.html?_nkw=&_armrs=1&_ipg=&_from=
At 3 packs, get a 4th pack so you can ride 12s lol.
It’s getting close to supercap money too.
Also bare in mined you need a psu with the caps and a 8.1v cc-cv buc converter to go with your super caps
Thay only deliver 1200amps the advantage is thay don’t heat up as much as my 6ah battry some other people above in this thread are useing 2 super caps in parallel at 1600 amps from my memory.
I can only offer my opinion of x is better than y because z or joe blogs has used x and says it works. How much to spend and on what part is down to each pension. The same argument can be to why are we useing 63xx motors when 50xx were fine or q30 over r25
I have here a 6s 10Ah Lipopack from my first build and they’re deadchunk, cuz I forgot to put em’ to storage. (four months) 
100 bucks down the drain. 
Have hurried up, all open orders just went out 
Seems that my kWeld business is causing troble for Hobbyking… I have testing newer models / from oher brands / possibly with XT150 and 8AWG on my todo list. All that’s missing is time 
(and batteries)…
It greatly depends on what you want to weld. You don’t need 1500A+ for 0.1 or 0.2mm nickel. Of course the more current the better, but you’ll also want to hit the price/performance optimum.
I would definitely get 2.
Once you’ve had a bit of practice, you will be able to weld quicker than one battery can keep up with and the battery will get hot.
With 2, you will know when to rest because your probe wires will get hot, but not the batteries 
Nobody wants a hot puffy lipo.
I start slow. I have already ordered a lipo. no second one.
Gone forever. This is my preferred alter ego 
I’ll remember this.
I made exactly that. Works on my malelectrics spot welder. I’m jealous of y’all with kwelds. Impossible to get at the moment here.
Used them on 0.2 tested pure nickel. Don’t have 0.3mm to test.
I’m looking hard at 0.3mm nickel plated copper. That would be brilliant.
I could bring you one in August, if you want. 
Negative on 3s1p. 3s2p get warmer than I’d like. (Warm to touch which isn’t great for a mass that large)
I connected cells with purpose made tinned copper foil crimps from an industrial supply joint. (I.e. I didn’t pussy foot around with mild sauce for series connections. )
Sorry for late reply.
@Mainflow sign me up.
5.5mm bullets should be also ok, right?
I have a shitton of that in my drawer.
Recommended to use as150 if possible, you need a cheap amazon heavy duty or hydraulic crimper really for doing the welding probes
I chose the assembled cables. So no big deal.
Check the manual Frank made, its really detailed and helpful
So you need ring terminals to affix the input leads to the Kweld unit. Can’t remember if they are in the kit contents. The example shown is XT150 connectors to the power source for big burst, if you use 5.5mm bullets your bottleneck May be there, depending of course on the ability of the power source.
Ive used xt90 in the past they can get hot under big pulses / continuous welding.
