However I also wondered how much if its info was dependant on the hardware in the laptop.
Thats certainly probable as any monitor just taking a voltage reading without measuring the voltage vs load over a significant amount of time and through several charging / discharging cycles are unlikely to be accurate.
My Sunny Island gives both State of Charge (SOC) and State of Health (SOH) of my battery bank.
SOC is a simple % charge of the battery along with a % of uncertanty which gets larger if the batteries dont get a full charge for a while. It does this by counting Ah's in and out of the battery but also re-calculates occasionally by measuring the voltage verses load if the battery has been under a constant load for a long time. It also seems to reset itself at 100% if the batteries have been given a really good charge.
SOH gives an estimate of the current capacity (when full charged) as a percentage of the original capacity of the batteries as manually entered (in Ah's @ C10) when the batteries were new. The manual says it needs several cycles to give an accurate reading of this. Interestingly this has only been as high as 96% even when my batteries were new but this could be because I had to make an estimate of capacity @ C10 as I only had the spec @ C20. After 7 months of use the reading is currently 95% so a loss of only 1% during this time is quite reassuring for me.
