There was a final report of this
IPEMU▸ trial, which I don't think has been reported here, though it's not easy to find it. It is available to anyone with a SPARK registration, and anyone can register with SPARK, but it's not for those with a serious hoop aversion. You may recall SPARK as being the document store for
RSSB▸ research. Most of that has now moved back to the main RSSB site, where (at least I found) the same registration is valid. SPARK still exists, for other rail industry stuff that doesn't clearly belong somewhere else.
So, the IPEMU final report is a network rail document,
Ref: RMVP/RPT/0448; Issue: 1; Date: 05/10/2016 "Independently Powered Electric Multiple Unit (IPEMU) Trial Report".I can't quote a short summary or conclusion, as there isn't one. The conclusions section refers back to the conclusions in the other sections, and is hard to follow without those. That's partly because the trial running of the train was only a part of the battery testing, other types were tested statically for comparison.
Remember, too, that this was an experiment, not a prototype. The train did not represent anything that could be built in quantity and put into operation; the aim was only to provide practical data for future designs. So exactly how well it ran in service is not really the point of the exercise.
On that basis, it's not a surprise that the (lithium iron phosphate) batteries in the train had too little cooling, and heat built up during the day until it needed a rest in the afternoon. Otherwise the train ran with no serious faults. Some design issues were identified which will need to be solved, notably how to control load sharing in parallel cells.
Two other battery chemistries were tested on the bench, but both were further from a usable product. Lithium titanate was assessed as likely to fit the requirements, with some more development. While it has lower energy density, it has higher power density, and the high power demand is the key parameter in trains. Molten sodium was also tested, but was less advanced and could only be rated "promising" at this stage.