I cut the power remotely and let the batteries drain, and I get the following at 18.6V, after the lowest priority POE power cycles
name: ether2 ether3 ether4 ether5
poe-out: forced-on forced-on forced-on forced-on
poe-out-status: powered-on powered-on powered-on powered-on
poe-out-voltage: 18.6V 18.6V 18.6V 18.6V
poe-out-current: 492mA 436mA 103mA 48mA
poe-out-power: 9.1W 8.1W 1.9W 0.8W
Obviously the values change, and I only reported an single moment, but it more or less gives you an idea of the relative amps. The watts don't change when the voltage changes, because
When I put lock an interface to 100Mbps FD instead of letting it auto-negotiate Gbps, the current drops by approx 60mA at 18.6V
1.116W = 18.6V * .06amps
And in practice I also see approx a 1 Watt drop, also, which seems to confirm the theory.
I have not tested the EXACT same load on the power box 10/100. But I can tell you than I never saw this problem, and I have run a few prisms on them, with no problems. I do not have enough old Power Box to test, as I am using all of them now in production...