Look, I love lithium batteries as much as anyone, but the range really is a huge problem. If you take a look at the real world places that the existing diesel locomotives serve (on non-electrified lines) you have a lot of places where you're basically using one or two trainsets to go back and forth a rural line. They usually don't sit in stations for more than a minute or two, maybe 5-10 mins at each end. If each one is out of service to charge for 30 minutes once an hour, you're either demolishing the schedule or adding significantly more trainsets ($$$$).
Many lines connect rural to less rural places. As the train will get closer to the less rural place, it will start running under the wire. At the rural end of the line there can be a dedicated charging station for layovers. This way, there are plenty of opportunities to charge the trains.
In Germany, a very high percentage of Diesel Services could be replaced by trains having about 50km of autonomy - and for the rest it would be possible to fill the gaps using only a relatively small amount of electrification.
That's simply not how the lines are usually built, unfortunately [0]. In general, electrification was done for entire rail lines. If you look at maps of non-electrified rail, it's a relatively small amount where you have a sufficiently long electrified section near a station to charge. And usually, at the end of the line, you don't have enough time to get a good charge in.
Certain regions of Germany are an exception, partly due to their early electrification of the rail, then subsequent damage in WW2, then strange rail layouts, but if you look at non-electrified rail maps of the Netherlands, France, the UK etc it will be extremely clear that battery trains wouldn't work well.
Part of the reasoning is that you want these massive batteries to last, so you're going to want to charge at the fastest around 1C, aka 1 hour for a full charge. Turnaround time at the end stations being usually around 5 minutes for these services, your choice is either to absolutely destroy your schedule, fork up far more $$$$ for more material or ignore battery rail.
Look, if they made economic sense, we'd already have electric locomotives - the technology is extremely simple, just toss a bunch of batteries into a box; the engines themselves are already electric. Similar batteries to electric buses, too. But while the economics of electric buses do make sense - and you see electric buses in most of the world's cities today - trains running on batteries really don't make sense in most cases. That's why you don't really see them. Out of the nearly 2000 Stadler FLIRTs that are running across Europe, zero of them run entirely on batteries today - and there will only be a projected 55 in 2023 (!) in one region of Germany.
Yep, there's your problem...
Look, I love lithium batteries as much as anyone, but the range really is a huge problem. If you take a look at the real world places that the existing diesel locomotives serve (on non-electrified lines) you have a lot of places where you're basically using one or two trainsets to go back and forth a rural line. They usually don't sit in stations for more than a minute or two, maybe 5-10 mins at each end. If each one is out of service to charge for 30 minutes once an hour, you're either demolishing the schedule or adding significantly more trainsets ($$$$).