I couldn't answer about the cost note, but for now batteries have to work coupled with traditional wires. That's the way they do in Nice that's the only city in France to have opted for batteries for a couple of short sections of their single line complete so far. Most the line is supplied by a catenary that reloads batteries while powering a tram. Then within downtown Nice where wires were regarded an issue to the streetscape, batteries take over for a little part of the ride. I saw no complaint about this system. In fact it's locally so successful that Nice is to literally quadruple the size of their current tiny network (again, made of one single line for now). Batteries might well be an interesting option, because it's definitely evolutionary. I mean serious improvements are expected in that technology.
As for 3rd rail, I find the term a little confusing when it comes to streetcars/trams, because it's something different from the regular 3rd rail of a heavier subway train for example. For LRT, the system is more sophisticated precisely because of absolute safety requirements. Some on here may remember what we had once read on Wiki.
Quote:
Unlike the track-side third rail used by most metro trains and some main-line railways, APS (alimentation par le sol) does not pose a danger to people or animals and so can be used in pedestrian areas and city streets.
APS uses a third rail placed between the running rails, divided electrically into eight-metre segments with three-metre neutral sections between. Each tram has two power collection skates, next to which are antennas that send radio signals to energise the power rail segments as the tram passes over them. At any one time, no more than two consecutive segments under the tram should actually be live.
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That's really some good stuff that's been hard to operate at the beginning in Bordeaux that was the first city worldwide to implement it. It works fine now, and it's what most serious French places are choosing for their downtowns. However, I don't know whether it could stand cars going over it, over and over, constantly. It's designed for pedestrian/bike safety and runs only in dedicated lanes in French cities, I believe.
In short, both options are quite likely interesting, although 3rd rail seems more powerful for now. I think getting rid of catenaries is an ambitious and forward-looking choice for LRT. Clearly the best. Speaking of that, I find it somewhat messed up that
every single LRT thing in Paris is still
entirely on catenary while some ridiculously smaller places like Tours got their more advanced 3rd rail showing off and teasing us. What the heck, RATP?