Don't know if anyone is interested but they've started producing a new Lithium battery, rather than Lithium Ion, their using Lithium Iron Phosphate (LiFePo4)
It's cycle life is twice as long as a Lithium Ion battery (so 4 times as long as a SLA battery). Only weighs slightly more than the older Lithium batteries but won't spontaneously burst into flames at the slightest miss use!
It's identical to Lithium Ion batteries in every other way.
As it's not so hazardous, it's not so expensive to manufacture/dispose of so prices are cheaper.
I've just bought one from here - https://www.batterym...SortBy=Cheapest
12v 12Ah battery with delivery for £99.99 (plus free charger)
There might be cheaper prices out there but this is the cheapest I found.
The price of a 10Ah Lithium Ion battery on THL store is £144.99 and the 14Ah is £158.99 (which is pretty cheap for an Ion battery)