[Sunking]

Ignoring everything except Battery Internal Resistance, what is the best battery?

• Lithium
• Lead Acid
• NiCd
• LiMh

[MN Driver]

... Read what you said as being 'ignoring internal resistance' which is the best, so I'm removing what I said to make a proper response.

Lithium Cobalt chemistry has some of the most powerful cells I've ever seen.
Saft has the most powerful LiFePO4 I've ever seen and some incredibly powerful LiCo chemistry cells too.
NiCd and NiMh, I haven't really seen anything take over 20C very well, not to say it doesn't exist.
Lead-acid some of the Odyssey AGM cells that Wayland uses seems to be about the best in the lead-acid world but I don't think the best of AGM today beats anything lithium now.

[Sunking]

Originally Posted by MN Driver

Lithium Cobalt chemistry has some of the most powerful cells I've ever seen.

I am not exactly sure what you mean by most powerful, perhaps energy density, but Lithium Cobalt has considerable higher internal resistance compared to NiCd and NiMh. I would think internal resistance would be a huge factor with respect to EV applications to deliver as much current as possible with the lowest voltage sag.

[rwaudio]

I don't have much to add except that my LiFePO4 A123 20ah pouches measure 1-1.5mohms. So for a 200ah pack that's 0.1-0.15mohms, an expensive pack, but minimal sag. (I won't have a 200ah pack though)