I'd heard that adding two percent silver to the metal grids of lead acid batteries prevents the Brown (Positive?) plate grid from progressively dissolving with charging and extends the life by at least double.
Caterpillar used to do this for their old earthmoving machine batteries and a guy I know has had his in a tractor on constant solar trickle charge for 28 years now with occasional weekly use.
I'd like to see more NiFe cells for sale too, it should be possible with modern high purity materials to reduce the self discharge rate and increase the charging efficiency. There are examples of NiFe's that still work fine and are over 100 years old. And they are made from relatively non toxic metals.