Can you give more detail, Roger? Which design, all-up weight, gauge and what size batteries?
Four similar springs except they are only 1/4" diameter reduced to about 3/34" long suit my shunter – it is 3 1/2" gauge and 1 7Ah lead acid battery, but with lead ballast so it weighs 28 lbs.
If your is the same gauge with two similar batteries but no ballast I would guess that six such springs could be more or less Ok, although 5/16" springs will compress more easily than 1/4" diameter.
Neil