Hey Ben - did you know - that one of the leading Tech Team on the Tesla started first with a 944 Porsce with two motors linked (either by belt or chain, can't remember) but Lead-Acid Batteries! Lots of GO! But not very far! That lead to conversations, connections, and the move to the 18650 cells and the formation of a team building the first Tesla Roadster!
Sure - they have a head start - but there is till room for the rest of us to Blossom!
About the details - I think you mentioned the four new Yellow tops cost you $800. That is for a 48V Pack with a (Theoretical) Energy storage of 55 Ah. Since I can not get the hard data for the Yellow tops, and can only guess, I used a reference of the Power Battery specs for a 55 Ah AGM from a UPS Set I got from work.
They are rated at 55 Ah (20 Hour) but just 33 Ah for one hour, and even that is pretty good for PBA! Also - just over 20 Ah for 2 hours (20.5 Ah) - this from a battery weighing it at 44 lbs: Power-Battery_PRC-1255S.jpg.
Per my Whitepaper #1 - the 40 Ah ThunderSky Cells can be bought from a fair number of places for $50 per cell, and at 4 per 12V set = the same $200 per 12V, but - they can deliver a 40Ah result in the one hour time frame.
Both of these energy values are for a 100% DOD for which the Lead Acid is good for about 300 - 400 cycles, but the TS for 1000 cycles. Dropping back to 80% DOD - still gives you 32 Ah from the TS cells, and now you get about 2000 cycles, vs. the 3-400 cycles for the 33Ah from the Power Battery. Other battery specs attached for additional references.
Also attached - a fairly easy to find Lead acid AGM - the BB Brand, EP33-12.
33 Ah at the 20 hour rate, but just 19.2 Ah deliverable in the 1 hour time frame of reference that I use in my whitepapers!
So - the BB would require two of them to deliver the energy equal of four of the TS-40AH cells in a 12V pack.
Refurb UPS sells knock offs of them for $70 - so yes - they would be cheaper than 4 x $50 TS 40Ah cells ( a bit!)
Atbatt - sells a variety of them for a good price too!
But - back to yellow Tops -
The Robot Market Place sells them for $249.99! Just a little over what wall mart was selling the Blue Tops for here in Toronto!
On the Other Hand -
WallCann - sells them for ..... $365! So your price of $200 each was a very good price! And looking at walmart.com - I can't even find them!
Surrette data in next post - too much data for one post! Robert