BE55 PLT ON IFR FLT PLAN; INFORMS ZBW THAT HE HAS LOW VOLTAGE ON BOTH GENERATORS; AND IS TOLD TO LAND AT SWF.

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I AM FILING THIS RPT JUST IN CASE ANY REGS WERE VIOLATED. ON AN IFR FLT PLAN FROM N27 TO SFZ. APPROX 1/2 HR INTO THE FLT THE VOLTMETERS ON BOTH ENGS STARTED TO DROP BELOW NORMAL -- ALL OTHER EQUIP WAS FUNCTIONING NORMALLY BUT AS A PRECAUTION I SHUT DOWN ALL OTHER 'NON' NECESSARY ITEMS (HEATER; PITOT HEAT; ETC) IN ORDER TO CONSERVE VOLTAGE. I ALERTED ZBW AT THAT TIME. MY DEST SFZ WAS IN CLR WX AND UNLIMITED VISIBILITY NO CLOUDS; AS WAS ALL OF THE EAST COAST THAT DAY. I TOLD ATC THAT I WOULD KEEP THEM ADVISED OF THE SITUATION. A FEW MINS LATER ZBW REQUESTED I LAND IMMEDIATELY AT STEWART ARPT APPROX 3 MI FROM MY POS. I WAS ASKED BY ZBW WHETHER I WAS DECLARING AN EMER. I REPLIED IN THE NEGATIVE; THAT ALL SYS WERE FULLY OPERATIONAL. STILL I COMPLIED WITH THEIR REQUEST. I LANDED UNEVENTFULLY AT STEWART AND PROCEEDED TO EVALUATE THE REASON FOR VOLTAGE DROPS ON BOTH GENERATORS. NO ONE WITH ANY QUALIFICATIONS TO DIAGNOSE THE PROB WAS AVAILABLE AT STEWART. ALL BUT ONE OF MY PAX HAD RENTED VEHICLES TO RETURN HOME. AFTER SOME TIME TRYING TO DETERMINE THE PROB IT WAS DETERMINED THAT THERE MOST LIKELY WAS A STUCK RELAY BECAUSE UPON RESTARTING THE ENGS THE CHARGE RATE WAS NORMAL. HOWEVER WE ELECTED TO FLY THE ACFT HOME TO HGR VFR. IN CASE ANY FURTHER RECURRENCE OF THE CHARGING PROB WE ELECTED TO FLY WITH THE GEAR DOWN. EVEN THOUGH THEY CAN BE LOWERED MECHANICALLY; THE FLT BACK TO HGR WAS UNEVENTFUL UNTIL ABOUT 1/2 WAY THERE WHEN THE VOLTAGE DROP OCCURRED AGAIN. WE WERE ABOUT 1 HR AWAY FROM HGR. RADIO FAILURE OCCURRED BUT WE WERE ABLE TO RECEIVE LIGHT SIGNALS FROM THE TWR AND LANDED SAFELY. BY BEING ASKED TO LAND AT STEWART ARPT BY ATC SEEMED A BIT OUT OF THE ORDINARY BUT THINGS TURNED OUT WELL ENOUGH. WE WERE APPROX 30 MINS AWAY FROM PAWTUCKET; RI; WHERE WE KNEW THAT A GOOD REPAIR FACILITY WAS AVAILABLE. PERHAPS IT WAS MORE PRUDENT TO LAND AT STEWART. JUST WANTED TO MAKE SURE I DID NOT VIOLATE ANY FAR'S IN THE PROCESS. SHOULD I HAVE CANCELED IFR AND CONTINUED TO MY DEST TO AN UNCTLED VFR FIELD; I DON'T BELIEVE IT WOULD HAVE INCURRED ANYMORE RISK. AND MOST LIKELY THE VOLTAGE PROB COULD HAVE MORE READILY BEEN DIAGNOSED. WE HAD ONBOARD GPS NAV INDEPENDENT FROM ACFT SYS.