The piece by Brigadier John Lewendon is as definitive as I believe you will get. He says:
The dearth of information about a Gunner presence in the Netherlands East Indies in the earlier part of 1942 was brought home to me in the RA Library Archives. This is not surprising when it is remembered that:-
a. No Unit War diary has survived from the Java/Sumatra campaign of 1942 - precious few survived from the Malayan Campaign.
b. Such campaign accounts that do exist were mostly written over three years later at the end of a traumatic period as POWs of the Japanese in the most appalling and bestial conditions.
c. The events themselves lasted for barely four weeks.Brigadier Lewendon was at one time the Historical Secretary of the Royal Artillery and has written extensively on the Royal Artillery and the piece comes from his research in the RA Library and Archives so I'd say he has covered all there is to know about this difficult time.
I have already highlighted what I can find at the National Archives for the regiment and the battery (Brig Lewendon notes that none survive for the relevant time!) so there is no "history of 89 baty TA" that you ask for. I've looked for National Archive material for 78 Battery but nothing comes up that would answer the question about the two troops (I have seen one ref that says only B troop went with 78 Battery). The number of troops in a LAA Regiment was not always the same, I've come across three and four although the most usual was four troops of 4 guns each.
I note this reference in the Imperial War Museum:
http://www.iwm.org.uk/collections/item/object/1030003821is the papers of an officer who served in 89 Battery in Java. You should contact the IWM staff to see what is involved in seeing these papers.
I fear the detail you are looking for is the sort of nitty gritty that only deep research with original documents will uncover and my view is that there is unlikely to be anything out there that hasn't already been referenced. Contact with FEPOW as Nanny Jan has recommended would be a good idea.
MaxD