Bad batteries or something else?
For whatever reason, Universal diesels used on the P-27''s have had intermittent starting problems sometimes traced to smallish wiring at the starter solenoid. But first, do check the batteries with a digital volt meter to make sure they are charged properly. Even though the one is about a year old, it could be shot if it wasn''t kept charged over the winter, water level wasn''t kept above the plates, etc. If you don''t keep a digital meter onboard, buy one and use it regularly. They aren''t all that expensive.
If the batteries are OK, you need to check out the engine. There''s a P-27 email list I can put you on if you''d like so that you can ask your question there. I have a P-27 with a Westerbeke, but lots of folks on that list have Universals and have addressed this problem. Let me know if you''d like to join our list. It''s a good group and we have exchanged lots of good ideas and info.