I rang Fiat Assist and got a new battery. Of course they didn't have S/S batteries in the van so he fitted a conventional one, but it's up from 63Ah to 110Ah
To my amazement S/S worked right away.
I gave it a good thrash in the hills much like I had on the last tank and so far I'm seeing 5.2-5.8l/100km vs the last tank's 7.0. I'd wager driving style is similar but I've got the A/C on now where as the last tank was in cooler weather. S/S isn't really in play here as it's all country miles so far.
On the plus side, with my solar charger and a 110ah battery, I've now got a Micro PHEV, the car can make it all the way to the shops without the alt. kicking in
I haven't weighed it yet but it's the same physical size as the old one.