FYI: I've been informed, via email, by one of our retired engineers, Bigfootford, that a battery discharge caused by the loss of AC is common to many maintainers of this type and others. It is not merely a HF problem.
Sorry if this a duplicate. This is not a GFI problem per say. Using a GFI breaker is what is creating the situation. The GFI circuit works by reading the difference in current between the neutral and the load, downline. With a breaker this is often far away. The solution is: Use a regular breaker circuit, and extention cord with a GFI outlet at the end, near your load. Any GFI protection is set at the factory at between 2.5 and 5 ma leak before tripping. With a long circuit down-line, one goes beyond the tripping level. When having long circuit lenghts, it is preferable to use GFI receptacles over breakers.