@finbarr yeah, if this had lithium batteries it'd be an awesome little system. But then you may as well buy a big Ecoflow unit and the panel, or a 2.4kwh pack and a victron inverter and build a typical off grid system like the vanlife/tiny house people do.

@nigel I'm not sure it's hard to measure. I'm not even sure I'm discharging to 80%, it all goes off voltage except that drops under load so you have to measure the voltage when it's not under load. Maybe half a kWh or something?

@james In comparison I've got two 36Ah 12v batteries in my shed and in theory they should provide around 430Wh each for a total of around 860Wh. I've not measured them with a full discharge and I can't remember what I set the low voltage cut-off to on the inverter (I left it at whatever the default was for LiFePo4 batteries) so I've no idea if I'll get that much.

One disadvantage of Lithium batteries is that you can't charge them below 0°c and I think lead acid can.

@nigel lead acid has its own problems below zero... If they're low on charge they can freeze and burst open.