I’ve got a cat with 2 independent start
batteries. The alternators are hooked up to their respective start
batteries. The start batteries are hooked up via an isolation switch for “bridging” to the house (for
emergency start or
charging the house from the alternator). Each starter
battery is also hooked up to the house
battery via a
solar charger, which acts as a
cheap DC-DC
charger keeping the start battery topped off.
My port
engine has never given me issues. Fingers crossed that continues.
The starboard
engine will often fail to start. I checked the connections, replaced the start battery, replaced the ignition switch, and replaced the starter. The starter was the only thing that gave any noticeable improvement. But now the engine struggles to start. Especially on mornings after I’ve been on board the night before.
The battery is reading 12 and some bit volts at the instrument panel, but I think there is some parasitic draw on the starboard start battery. This morning, after using 150 amp hours overnight (720 Ah
AGM bank), the starboard
motor would not start. The first attempt you could hear the starter kick over, but then nothing. Attempts 2-4 resulted in nothing from the starboard side.
After I started the port engine and connected all the bypasses and let things run for 15 minutes (to possibly charge the starboard side), the starboard engine kicked on straight away.
In terms of confirming this suspicion, the next time I’m on the
boat and the starboard doesn’t start, I’ll swap the batteries and see if I can recreate the problem on the port side. I could also buy a
lithium battery jumper and try that out.
If I’m able to identify a battery issue - how do I go about
tracking down the parasitic draw? The isolators are off (open), so the only things connected to the start battery should be the
windlass (fused open), the
solar charger, the isolated house bank, and the engine.
I’m leaning towards battery issue because we haven’t yet had a problem getting the engine started when returning to the
boat after a couple days (solar keeps us topped off) and the afternoon also seems to be a perfectly fine time for the engine (again because the solar has been pumping in all day). The previous owner also replaced this start battery in 2020.