Specifications of battery:
The changhong batteries sold for photovoltaic installations are "rated" at 0.2C rate. The details of this might be gleaned from the marketing brochure they give out.
Power to weight, energy density, those don't really matter here.
Capital cost is a paramount issue. Lead acid batteries used in solar by consumers (VRLA) cost about $0.2 USD per Wh. We should be able to beat this hands down, judging from materials costs. Several of the currently inaccessible documents describe in their abstracts practical Nife batteries that the (well informed) authors expect to cost less than $0.06 per Wh after all labor etc., on a mass scale.
Efficiency is also important, see related page section of main nife page for calculations on the impact of efficiency of the battery on total system cost. summary: If solar collector is $ 2 per watt then if half of the energy delivered to the user needs to be drawn from the battery then a 65% efficient battery has an inherent cost of $0.2 per Wh due to the increase in the solar collector that is required to compensate for energy wasted. The cost of the battery itself is dwarfed by that. The energy isn't free.
Lifetime has a major impact on the effective running cost. Batteries all have a running cost as they do not last forever. If the battery lasts 4 times as long as lead acid but the capital cost is exactly the same, then the running cost is 1/4 that of lead acid. This ignores the interest rate and a more detailed check should be done: the battery of capacity CAP gets purchased at time A for cost B ($/Wh). It loses capacity with time according to formula 1 (given the useage pattern we are expecting). The capacity becomes inadequate at time C. It then needs to be replaced or rejuvenated at cost D. All cost after this are ignored. Find the Present Value at time A in dollars per watt hour of battery. (the amount of money which has to be put down at time A to both buy the battery and pay for the maintenance during the period A-C.) Now do the same for the lead acid capacity loss formula, formula 2, and for a variety of battery capital costs.
We know what the useage pattern is, so we speak in terms of chronological lifetime, not charge/discharge cycles.