Dead port side battery

C

Cutty22

New Member
Aug 2, 2016
8
Lake erie
Boat Info
1998 310 sundancer
Engines
Mercruiser 350s alpha outdrives
Last weekend my port side battery went dead had to use emergency start called a mechanic because the batteries were only a year old. He replaced both batteries. I went to the boat three days later and same thing dead again? I have no idea? Please help!!
 
Are you turning your battery switches off when you leave the boat?

Welcome to CSR!
 
Cutty22 does the boat have a good battery charger onboard? I would think the battery charger would keep it up unless you have a bad charger.
 
The charger is showing on the needle that it is working? And yes I shut my battery main switches off when I leave
 
Cutty22 said:
The charger is showing on the needle that it is working? And yes I shut my battery main switches off when I leave
Click to expand...

Maybe a stuck float on a bilge pump? With the battery switches off the only thing that can normally run is your bilge pump. A PO (or you) could have added something else direct to the batteries... like stereo equipment?
 
I have not added any new stereo equipment at all and the strange thing is that I run the boat at full speed for about a hour and as soon as I shut both engines down you would think that it would stare but it just clicks
 
If there was a drain....the charger should have still kept up. Did your mechanic check the charging voltage before he left on that battery bank? I suspect the original charger might be the problem.
 
I don't think he did but the charger is what I'm starting to lean towards
 
Cutty22 said:
I have not added any new stereo equipment at all and the strange thing is that I run the boat at full speed for about a hour and as soon as I shut both engines down you would think that it would stare but it just clicks
Click to expand...

The battery isn't getting charged. My previous post was based on being connected to shore power. This indicates an alternator problem. Without an alternator the bank associated with that alternator will drain based on the engine electronics until the battery is exhausted. Same diagnostic....compare the charging voltages on your battery banks with the engines running (your mechanic should have done this) and you should find the problem.
 
Need to measure voltage at the battery with the shore power on and off to verify the charge is making to the battery. There are fuses along the way, so if blown, no charge makes it to the batteries. Should be in the 13.5-14.5 volt range when the charger is turned on, 12.8 when off.

If you ran the engine to charge the battery, it only charges the battery selected at the battery switch (unless you have an ACR).
 
I'm pretty sure he has three batteries isolated by two battery switches. One battery takes care of the port engine and the other two are tied together for House/Starboard engine. The alternator for each engine is isolated to its respective bank. The shore power inverter takes care of managing each bank electronically. From his last post, it seems to point more toward the alternator for the port engine. Perhaps it is a loose connection or a blown fuse but checking the port battery voltage with the engine running and at rest should provide the necessary clue.
 
But would the alternator drain the new battery just sitting there for three days?
 
I just had a similar issue with a dead batter and when I put my hand on the red wire coming off the alternator, I found that it was broken at the connector. Easy fix, thankfully, and definitely something worth checking.
 
I checked them over the weekend because on another boat I had the fiber insulator washer broke into pieces and the alternator went to ground
 
Let's rewind the tape.....

1) Is it on Shore power while it is sitting for three days?
2) If it is not, is the port side battery switch in the "Off" position?


The Port side battery and switch are isolated from the Starboard bank. When you press the Emergency Start switch, you temporarily bridge both banks to start the Port engine. Depending on your answers to the two questions.....the battery for some reason appears not to be holding a charge. Either it is incapable of doing so because it was damaged (possibly by over charging or undercharging) or it isn't being charged at all. A simple voltage test should eliminate charging as an issue.

If you have 13.5-14.5 volts with the engine running measure at the battery.....the alternator is fine.
If you have 13.5-14.5 volts with the boat hooked up to shore power .......the charger is fine.
If you have less than 12.8 volts with shore power and the engine off .....that is a problem.

It is possible that you have a significant drain on the Port Battery at rest. It's weird but possible (so is having a couple of new batteries go bad). Is there anything hooked up to that battery that doesn't go through the battery switch?
 
Yes it was hooked to shore power and both battery switches turned off
 
So that points to the port battery not being charged (or not holding a charge). It would appear that the problem is present both on shore power and when the engine is running which points back to a wiring/fuse issue. I am willing to bet that if you did check the voltage on the battery.....the voltage would remain unchanged in any operating mode (shore power, engine running or at rest). The job for your mechanic is to find out why that bank isn't charging.
 
To help you and your mechanic sort through the wiring:

http://rnr-marine.com/images/Sea-Ray_310-Sundancer_1998_Owners-Manual-Supplement.PDF

Page 22 shows the DC wiring for your boat. If you follow the alternator wire for either engine it goes to a rectifier. From there it goes to the Emergency Start Solenoid where it connects back to the battery. Somewhere along this path there is a problem for the port bank. By comparing results off the Starboard engine/bank....he should find the problem.
 
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