Accurately monitoring lead-acid battery state-of-charge would help with the long-term sustainability of off-grid renewable energy systems.
There are a number of ready-built products already available, mainly for the recreational vehicle market (eg. boats) and are relatively high cost (too high to include within a small off-grid power supply system).
There are also a number of ICs (intgrated circuits) which can perform this function. I wanted to review the few that I had heard about and see how applicable they might be for an off-grid battery monitor.
This ties in with my open-source charge controller project and also the battery monitor project, which has been on my list of things to do for a number of years. The addition of battery monitoring capability would be one of the most useful additions.