I have a USA F3 A-B unit that I run from a TE plus batteries.
For normal radio control battery power there are three issues to running sevaral locomotives from a single throttle/battery pack.
1) will the radio receiver handle the amperage draw: Clearly, a heavy train with multiple locos will draw significant current especially if the locos are big multi motored diesels. Both RCS and Aristo (the TE trackside) make units sufficently large to handle a current draw of 10A though keep in mind that the trackside is a pretty big board to fit inside anything but a trailing power car. I cannot comment on other systems as members of our club (OVGRS) do not use those other systems especially in a power car driving multiple locos.
2) are the batteries "big" enough: There are two forms of big in this debate ... one is, do the batteries contain sufficient amp hours of charge to actually power the locos in question long enough to make the run worthwhile. Since our ops sessions typically last about 2 hours every saturday morning (and nobody runs flat out the whole time) we typically use run times of about an hour and a half as a benchmark. Since there are custom battery packs available with 10000 mah and more, sizing the battery to the need should not be a problem. The second aspect to consider is the current draw. Most battery packs made up of AA cells for example do not take kindly to rapid continuous high current draw. C or D cells are more appropriate for that. Experience with LI ion cells is just now accumulating ...
3) will the locos and MU cables handle the current: If more than 5A will be pulled at a time, there will be tremendous electronic forces placed on the cables and connectors. Beware of meltdowns from wiring components that are too small. Also, if a locos internal wiring is being used to pass the current to other units in the MU, it could also be undersized. Aristo protects its locos with a poly fuse making them useless for MUing without rewiring. Jumping around the polyswitch can lead to trouble where the wiring is too small.
These installs are not light. My F3 B unit with a TE Travkside board and a big pack of sub C cells is very heavy ...
http://ovgrs.editme.com/F3B to see a writeup with pics.
Regards ... Doug