What is the next logical step?

[Cbr1000dude]

My 2007 Larson 274 Cabrio has a strange electrical gremlin that just blows my mind when troubleshooting, so perhaps someone could take a stab at the next logical step.
It will start right up with the Perko switch on both or #2, but just clicks like a dead battery on #1. Both batteries were new in 11/19.
I really don't want to lug two new batteries down the dock only to find it doesn't solve my problem.
I can't even seem to figure out which battery is the bad one. The volt meter is labeled port and starboard, but both are on the starboard side. The Perko switch is labeled 1 or 2. The breaker panel in the Perko switch box has battery charger 1 and 2. I only see one battery charger labeled 20 amp hidden behind the holding tank hoses and lots of wires, can't see where the wires from it lead. I not sure if both batteries are getting charged from shore power, but both charge with the engine running.
I drew a diagram.

 

[Scott Danforth]

step 1. load test your batteries
step 2. clean all your connections

you only have 1 engine and two batteries, correct? yes or no

Is there an ACR? yes or no

if yes to both, you are charging thru the perko switch from the alternator.
your shore power (AC) should be connected to both batteries.

 

[alldodge]

Unplug the Bat charger
Disconnect one of the Bats Negative lead
See if the same crank situation happens, and if it does reconnect the one and disconnect the other and try again

Once you know which Bat does it, swap the Bats location or its leads to find out if its the Bat or the Bat switch

 

[dingbat]

Both batteries were new in 11/19.

Means nothing. Marine Batteries typicaly die from abuse, not age.

Step #1 Make sure battery charger is off and crank the starter for a couple of seconds to burn off the surface charge on the battery.

Step #2 Measure voltage on both batteries. Should be between 12.6 and 12.7 volts.

Step #3 If both batteries are above 12.6 Volts, check voltage of each battery while cranking the starter. The voltage on both batteries should in theory, drop equally.

Interrupting the results is the tricky part....if the voltage drops below 9.5 V you have a weak battery. If you have a bad cable/connection, the voltage in that battery will not drop as much as the one with a good cable.
Either way, this test should at least identify the problematic circuit/battery.

I not sure if both batteries are getting charged from shore power, but both charge with the engine running.

13 V with charger/motor running means the supply is working. Doesn't mean the battery is accepting the charge

 

[Cbr1000dude]

Means nothing. Marine Batteries typicaly die from abuse, not age.

Step #1 Make sure battery charger is off and crank the starter for a couple of seconds to burn off the surface charge on the battery.

Step #2 Measure voltage on both batteries. Should be between 12.6 and 12.7 volts.

Step #3 If both batteries are above 12.6 Volts, check voltage of each battery while cranking the starter. The voltage on both batteries should in theory, drop equally.

Interrupting the results is the tricky part....if the voltage drops below 9.5 V you have a weak battery. If you have a bad cable/connection, the voltage in that battery will not drop as much as the one with a good cable.
Either way, this test should at least identify the problematic circuit/battery.


13 V with charger/motor running means the supply is working. Doesn't mean the battery is accepting the charge

Thanks for all the replies so far.
When I bought the boat, the po said to turn off the batteries each time I leave the boat and plug in to shore power. Today I talked to a Volvo Penta mechanic who said to leave the Perko switch on "both" to charge both batteries. So, I went out to the boat and did that. I'll check the charge state tomorrow by trying to start on #1 on the Perko switch.
Weird thing though, when I first did the battery voltage flip switch with the dc main off, only the starboard side said 14 volts, (shore power and battery charger on), the port said zero. So I turned on the dc main, and both sides said 14 volts, then I turned off the dc main, and to my surprise, both sides still said 14 volts. I don't see how this makes sense. This has happened before, but I doubted what I saw. I was real observant today and wrote down the sequence. Is this related?

 

[dingbat]

So I turned on the dc main, and both sides said 14 volts, then I turned off the dc main, and to my surprise, both sides still said 14 volts. I don't see how this makes sense.

That's the "surface" charge I noted above.

BU-804c: Acid Stratification and Surface Charge

BU meta description needed...

batteryuniversity.com

 

[Cbr1000dude]

Wow, that is a great article on surface charge!
Thanks.

 

[ejnichol]

Its a real good idea to study you wiring closely. Clean up any tangles by rerouting, gathering up excess and zip tieing, shortening if practical.

Use a volt meter to test if charger power is going to each battery when battery switch is in different positions. You should get see positive voltage increase at terminals with charger powered vs not.

On my boat the chargers are direct to battery regardless of battery switch selection.

My boat is similar layout to yours and was and is a maze of wiring. Cleaned up wiring to make safer. Easy to see why boat fires are a thing.

 

[Cbr1000dude]

After reading up on batteries, today I bought two new batteries and changed them myself, not an easy job. Now it starts right up on position 1 or 2. Yes!
The po had installed group 24, I got group 27 (higher cca) and it cranks much faster. This is a 8.1 engine. I'm not sure if bigger batteries were necessary, but as long as I was at it, why not. There is plenty of room. Battery 1 is the furthest aft on this model, and it only had 11.9 volts on the dock. Pretty dead.
The battery boxes and straps were shot too, plus one hold down bracket missing. I'll correct all that too.
It's a shame how some people treat their boats.

 

[Cbr1000dude]

Btw, keeping track of which wire or cable goes where is not as easy as I thought. I had one wrong. I figured it out today. I keep telling myself I will remember, right. Even photos aren't much help, the angle you need is always the one you didn't get.
I'm going to zip tie the four groups together next time before taking off any nuts. Really, I won't forget. Seems like I said that last time.

 

[froggy1150]

Loop a piece of masking tape like a flag and mark with a sharpie

 

[airshot]

Yes sir...I add many tags to my electrical wiring to keep things in order. I also zip tie all the wires going to each side and even add colored plastic tags made from old oil bottles ( red and black) zip tied on as well. Saved me many times from having to trace wires back or creating a short.