Steez has a good point. Even a small resistance in a high-amps connection (starter) can have a huge impact on starting performance.

As to plugging in at the house for overnight: While that might get around the problem, I would not want to go on the water with a battery in such poor condition as you have described.

The cells are being tested this morning after it had to be on the charger over night. I'm hoping that discovers something. It's really not an option, unless I have a very very long extension cord. We will see when they call this morning if they discovered an issue. I'll make sure the connections are good and clean when I reconnect whatever battery I end up with!

Pretty self explanatory! JMO!

If it tests good, and you continue to have problems with it i'll exchange it for you if it's less than 12 mos old. You do need to have all gps units wired to a switch to completely shut off any draw.

If the voltage drops that much when you crank it, the battery is no good. That's why they load test them to determine if they are good or bad. At rest voltage by itself means nothing.

To be clear, your electronics isn't causing this - it's just telling you the problem exists:

1) The electronics includes the ability to read voltage. It is simply reporting what it sees happen.
2) If you removed the electronics from the boat, I'm very certain that the same no-crank issue will still occur.
3) If you put a voltmeter on the battery (instead of attaching electronics) it would tell you that the voltage is dropping when you try to crank the outboard - just like the electronics is already doing.

The battery needs a load test more so than a cell specific gravity test, though I bet it won't look good by either test method.

In my Phoenix they have two switches that cut off power to everything when your off the water so it avoids issues like this. No power destruction to anything just the batteries are charging.

Group 27 is a little on the small side for cranking and running accessories isn't it?

Same with me,6 boats later.

Not sure what size outboard you have, but do some research on the required CCA's for your outboard. My dealer put a Grp 24 in my boat to crank a 250 Pro XS, barely enough juice to crank it. It did okay, barely, but last month I bought Grp 31 AGM from Batteries Plus, it is a beast.

Another thing to look at is the order in which items are on your terminals. The motor leads should be first. And no wing nuts. I read on another board to get a terminal to clamp on and put the motor on it, all others on the threaded terminal.

If it was me, I would get the dealer who sold you the battery to give you an exchange even if they say it is good.

Good luck!

I have a similar problem with my Triton. I'm the second owner of the boat so I'm not as familiar with how it was wired originally. I have do have a main cut off for power and turn it off after being on the water each day before putting the batteries back on the charger. When the charger is on I show 13.0-14.0 volts holding steading in maintenance mode. When I take the charger off I show voltage of 13.5 and dropping. Something is drawing power from my cranking battery with the main in the off position. I'm still trying to diagnose my problem but you may want to take a look at what the voltage is doing on and off the charger.

Sooner,

If you have a drain on the battery when the battery disconnect switch is in the off position (as you claim), then there are other wires on the battery. One of those sets of wires will be that drain - if there is one.

You mention that you see this when you "take the charger off" where I will assume that means unplug an on-board charger? How fast does the voltage drop? A flooded cell battery won't hold 13.5 indefinitely without a charger active as that's higher than 100% charge. Most battery companies state 100% charge as 12.70-12.75V for conventional flooded cell lead acid batteries.

The 13.5V reading you see after unplugging or removing a charger is a "surface charge" from the elevated charging voltage that will dissipate in a few hours. Measure your battery after a rest period of 8-12 hours - no charging and no known load. If you see 12.7V, you're good and there is no mystery load draining the battery. A battery sitting on a bench would do the same thing.

Thanks Flippin!

Absolutely what this guy says. The motor cables should have as much contact to the battery lead as possible. It needs to be the first cable on. Even better is what he says about a dedicated terminal to post setup. Accessories can come second. They pull nowhere even close to the amps that a starter will pull. Put surface area for conducting amos where it is needed.

As far as the group size? Depends on the motor size, number of pistons, age, fuel injection, ECM required voltage, etc. my little old Mercury is carbed and well broke in, and a group 24 is still too small. A 27 in my boat is minimum for the starter and helix units.