The constant pushing of 'SiO2' batteries is getting to be a bit absurd. It may be that they are a good option for Pianotuna's specific situation with very low temperatures, but for 99% of folks they are not a good value or performance option.
The 'facts' that are brought up to support SiO2 are dubious at best. You cannot take SiO2 to 0V 628 times. The manufacturer claims that you can pull the batteries 100% DOD (not 0V) 628 times, this is not really that different from regular AGM batteries. For comparison, most LiFePO4 manufacturers spec their batteries for > 3000 cycles at 100% DOD, so you get 5x the life from LiFePO4. You can now get a 100Ah LiFePO4 drop in for ~$600, so the price difference is not that much, and the value advantage is clear - less than 50% more for 5x the lifetime. If you build a DIY LiFePO4, then they are much cheaper than SiO2.
The rate of charge is another exaggeration - yes you can charge the SiO2 at C/4, but like all lead acid batteries you still have to deal with the absorb phase, so get the batteries back to full it will take 2-3 hours on top of what ever time it took in bulk. In comparison LiFePO4 will accept charge at C/2 or even C/1 all the way up to being full.
Anyway, this has been pointed out several times, but the same claims still get made. In general, if you want cheap then go with flooded lead acid, if you don't want maintenance, go with AGM, if you want the best lifetime value and performance go with LiFePO4. If for some reason it is really important for you to charge at -37C then go with SiO2.
