If you have a simple current limiter and are doing it the way we do it here, all you need is that, a power supply, a multimeter and your cell/electrode setup and a clock, watch or stopwatch.
You don't need to go high tech to make Colloidal Silver.
The reason Kephra built the silvertron is that normal people who aren't "tinkerers" like most of us on the forum are, would be at odds figuring it out, building their own current limiter (as simple as the LM317 limiter is),... They want "plug and play" but that comes at a high price.
Battery chargers aren't suitable for making Colloidal Silver because they're high current and designed for the voltage the cell or pack is at. Battery chargers are a very different animal. I just mentioned them as the battery gauge technique came from that area.
Any time you need to monitor current out or current in with detecting an endpoint which is the total number of electrons that have flowed (milliamp-hours or in the case of a Colloidal Silver cell, milliamp-minutes) and you have a processor at your disposal and the digital controlled current limiter and an analog to digital converter you can read instantaneous current with, battery gauging can be used to great advantage.
You simply integrate current over time and when the total reaches your target, which is what Faraday's law of electrolysis tells you in milliamp-minutes, you're done.
I'm not trying to dissuade you from your quest but you do have to think about some things.
You could be making Colloidal Silver as quickly as you can get the supplies together where you've spent maybe an hour tops building a current limiter.
OR, you could spend lots of time messing with a processor board, programming, designing/building other circuitry (because for sure a Raspberry PI won't have the current sensing/limiting circuitry you need - thats custom hardware design which, if you really want something like the silvertron, you're going to want to make the current limiter setpoint processor controlled), not to mention all the time you're investing (it won't be days - it will be weeks, minimum, if not longer to the point you've gotten it built, programmed, debugged and finally working correctly). Everything, when you start sweating the details, takes MUCH longer than your initial guess and nothing ever goes nearly as smoothly as you were thinking it would. NEVER!
I guess it boils down to one of just wanting a neat project to do because if you think about exactly how much Colloidal Silver you're going to make/consume a year, is all the above effort worth it?
Me, if I make a couple gallons of Colloidal Silver a year its a lot.
I can easily build a silvertron rehash but that investment in time, money, materials to make a couple gallons of Colloidal Silver a year a little more easily than how I currently do it is not worth it. As a one-up? Nope! If I were going to sell it as a product, so long as that unit commands a high enough price and the market is large enough (which I have an issue believing it is as its a very specialty device), perhaps it makes sense. But then, I have no intentions of ever going into the silvertron-esque business so for me its a waste of time.
Just to mention it to give you a heads up. Your choice.