Here you have one. There are two big classes of trays. The ones that cut the discharge when the voltage gets to .8V per cell and the ones that don't do it and discharge the cells to 0V.
The one you have on the photo has cut off. It's done by using a diode for each cell (notice the need to put the cells in a specific orientation due to polarity). The diode only allows the current to pass above a certain voltage (.8). When it drops below that the diode just cust the circuit.
The ones that don't do this allow you to put your packs in any orientation that want but may harm your cells if they are NiMh.
The Trinity ones don't have the cutoff at .8. Instead they have a very funny text printed on them:
NiCd Cells
Discharged when lights go out. Leave in pack for deep discharge equalizing
and
NiMh Cells
Remove pack when lights go out. Do not deep cycle
You see, if you forget the NiMh cells on the trinity tray you are deep discharging them and that's no good. A good tray forces you to place the cells in a certain orientation, but that's a minor problem whem compared with ruining 70 or 80 USD packs
Use a tray with cut off.
The idea of using a tray has to do with the need to have the cells discharged to a certain level. Not as a whole, but each cell individually. If you don't do that, on the next charge you may overcharge a cell in the pack and on discharge a cell may go so low that may invert polarity.
If you cells are in a similar state of charge/discharge the chances of this happening are very small.
Hope this helps.