The trouble was I forgot to bring our mains charger for the LiFePO4 battery packs in the Extenders.
That left our solar charging system as the only way to charge the batteries. Fortunately this is South Australia, and we get a lot of good sunshine, even in Autumn. The declination of the sun is enough though, that finding a nice 30 degree angle for the solar panel to sit on is a good idea. Fortunately we have such a slope just outside the lab. It is even North-facing. So I hopped outside and setup our 40W panel with the two Mesh Extenders. They each have a 120W hour battery, so 240W hours total is needed, which should take about 6 hours, but the batteries are already partly charged, so they should be charged enough by the end of the day.
Here they are charging happily without relying on any fixed infrastructure at all -- not even for energy. A very Serval moment.
Stepping back after I took the photo, I realised that I had inadvertently captured a great contrast between infrastructure and the low-cost, portable resilience that we are championing: In the background of the photo you can see the 250KW generator (including its perimeter fence to keep it and its fuel safe) and one of the University's data centres, together costing millions of dollars, and our few hundred dollars worth of resilience mobile communications gear lost in the vista.
Of course, the University data centre does much more than what our little buckets of radio can do, but sometimes you only need a little, and can't afford or sustain the big alternative.