The good news is that the CF mod almost doubles the battery life. I managed to record nearly 5 hr.
The bad news is that during the extended recording, there is a problem writing the DSD files. When recording a DFF file, the recording is subdivided into multiple files of approximately 1 GB each (approx 25 min), accompanied by a PROJ file which Audiogate uses to merge the files.
To test the runtime of the battery, I set it to record audio from my computer, and let it go till the battery ran out. On this 4+ hr recording, about half of the files were corrupted, and the PROJ file was not usable.
I repeated a long recording, this time with the unit plugged into an AC adapter, and let it go for 3 hr, which is a reasonable time for a fairly long concert. When I stopped the recording, it gave me a "Disk Error" and again, half the files were corrupted, and the PROJ file couldn't be loaded by Audiogate.
I suspect the problem is that the CF card doesn't write the DSD stream fast enough. The 133x Transcend card I am using is rated at 21.5MB/sec whereas the HDD and SSD write at 100 MB/sec.
So the conclusion is that as a 1-bit recorder, the CF card doesn't pass the test, so I probably won't use it in the field.
Success with the CF-mod!!
It turns out that the ZIF > CF adapter I used previously was crap! After success reported on head-fi.org, I tracked down the correct adapter and installed it. The price is about $20 on eBay, but if you are patient, you can get it from DealExtreme in Hong Kong for $6.30. It takes about 2-3 weeks:
http://www.dealextreme.com/details.dx/sku.11814
I tested it with a 133x 16 GB Transcend, and also an old PQI 2 GB card. Both worked!
Will do a battery test.