Battery Drain Help

[Gtown]

I have a 2007 Bayliner 246 Discovery 350 MPI with a B3. Two battery setup. I have been noticing that if I leave my boat for an extended time (2 weeks or more) my #2 battery will drain. To the point if will not turn over the engine. It has also dropped so low that the carbon monoxide detector starts beeping because of what I'm assuming is a low battery indication. Switch to battery #1 and fire up the engine and after 5 to 10 minutes the beeping stops (assuming the battery is now charged enough to stop the beeping - it will also turn over the engine now). Note: the battery switch has been in the off position when the battery drained. I have changed the battery with a new one and same problem (assume not a battery issue). I have also left the charger on and it has still drained. My understanding is that there are three things that could be drawing power if my battery switch is in the off position. 1. Mercathode, 2. Bilge pumps and 3. Carbon monoxide detector. My first question is would the Mercathode drain a battery in a 2 week period if not on a charger? The boat is docked in a saltwater environment. My concern here is that if left long enough it might drain both batteries. (Yes I do have a generator capable of charging the batteries and a battery pack for an emergency boost). If folks think that the Mercathode could draw enough power to drain the battery in this time frame I'm assuming the charger is not working. Next question is how do I test to see if the charger is working? I should also note I'm not 100% sure I have hooked the batteries up correctly (I took a pic from what the previous owner had done and continue to do the same hook up each year). If anyone has the correct diagram I would appreciate seeing it. Shouldn't the charger provide enough charge to counter any draw from the batteries? Assuming the charger isn't the problem I guess my next step would be to check to see if the bilge pumps are drawing power. Bilge area always remains dry. Again how do I test to see if they are drawing power? Any insight here would be appreciated. I should also note that everything on the boat is in excellent condition with no corrosion and is all original (10 years old). Realize I should replace my carbon monoxide detector based on the years. Could it draw enough power to drain the battery though? Sorry for the many questions but would be interested into folks thoughts on a singular problem or a compounded one. Thanks.

[bobofthenorth]

I'd say its pretty clear your charger isn't charging the battery that is going dead but if you want to confirm that just put a VOM across the terminals of that battery while you think it is charging. If it reads something like 12.xx volts its not charging. Under charge it should read 13.5++ volts.

[MonteVista]

Mercathode can draw a lot of power from the battery. Mercury manual also states this. If Mercathode is the culprit then you have a serious leakage issue between your boat and the shore and/or adjoining boats. You need to identify and fix this. Get hold of a loop type ammeter. WITH THE SHORE CABLE PLUGGED IN, check the current in/out the batteries, one at a time. Then UNPLUG the shore cable (GROUND conductor should not be connected to shore) and repeat the current measurement. If you see a significant current difference between the two this would indicate that a leakage current loop, involving the GROUND conductor exists and Mercathode is trying to oppose that and draws current from the battery.

Good luck.

[builderdude]

Verify your on board charger is delivering its charge current to both battery banks while the MBSS is set to the off position.

[Ricomoni]

I have the same year boat, your battery charger will not charge anything if the switch is left on the OFF or BOTH position. You must leave it on BATTERY 1 or BATTERY 2 position for it to work.

[Gtown]

I'd say its pretty clear your charger isn't charging the battery that is going dead but if you want to confirm that just put a VOM across the terminals of that battery while you think it is charging. If it reads something like 12.xx volts its not charging. Under charge it should read 13.5++ volts.

Simple and will give it a try. I do think its the charger. Thanks.

[Gtown]

Mercathode can draw a lot of power from the battery. Mercury manual also states this. If Mercathode is the culprit then you have a serious leakage issue between your boat and the shore and/or adjoining boats. You need to identify and fix this. Get hold of a loop type ammeter. WITH THE SHORE CABLE PLUGGED IN, check the current in/out the batteries, one at a time. Then UNPLUG the shore cable (GROUND conductor should not be connected to shore) and repeat the current measurement. If you see a significant current difference between the two this would indicate that a leakage current loop, involving the GROUND conductor exists and Mercathode is trying to oppose that and draws current from the battery.

Good luck.

Thanks for response. Are you saying the Mercathode will only draw a lot of power if there is a significant problem with the Ground conductor to the shore? How would this explain the draw if I'm not plugged in. I have had the battery go down when I have not been plugged in as well.

[Gtown]

I have the same year boat, your battery charger will not charge anything if the switch is left on the OFF or BOTH position. You must leave it on BATTERY 1 or BATTERY 2 position for it to work.

Builderdude is also eluding to this in his post. The green light indicating power is on in all positions OFF, BOTH. 1 and 2. I assume that if it is getting power (green light) it was charging. Are you saying that it needs to be switched to either 1 or 2 to charge? Can anyone confirm this? If so, wow "lightbulb moment"!

[Ricomoni]

Yes, It needs to be switched to 1 or 2 to charge!
Also, the Carbon monoxide detectors are always on even if you have the battery switch on the OFF position

[builderdude]

Actually if it was wired correctly the selection at the MBSS wouldn't matter. This schematic shows the general idea.

[Ricomoni]

I had the same problem he has (leaving battery switch in the OFF position). These are instructions i have read in my bayliner owners manual, instruction from the marina marine shop matches the the owners manual.
Since gaining this info five years ago, the problem was eliminated

[MonteVista]

Thanks for response. Are you saying the Mercathode will only draw a lot of power if there is a significant problem with the Ground conductor to the shore? How would this explain the draw if I'm not plugged in. I have had the battery go down when I have not been plugged in as well.

I did not know if you are/not connected to shore power. Leakage current corrosion occurs if you have two conductive paths; one through the water and the other (to complete the circuit) through the Ground conductor. If Mercathode does not detect leakage current it will not try to oppose it. I would still measure the current in/out each battery without the shore cable plugged in and also turn off the battery charger. If you do not measure any difference in current measurement and the current is very small very small, check the following;

1 - Make sure that the battery switch is indeed OFF
2 - Check the fridge(s); open the lid and check if the interior light is on. If the boat is wired correctly the fridge should not receive DC power when the battery switch is OFF
3 - CO detector should draw very little power. Do a test and unplug the CO detector when you leave the boat to see what will happen.
4 - If the bilge is dry, then the bilge pump is not a likely suspect.
5 - If, for some reason one of the batteries is bad, it may be drawing a lot of current from the other battery. If you have a battery isolator you should check if it is functioning properly and if its connections are good. If you have a bad isolator, one battery will discharge over the other.
6 - How the charger may affect things depends on how it is wired. As Bounty pointed out, if it is wired correctly, the battery switch position does not matter for the charger to charge the batteries. That is because, as his diagram shows, the charger is connected directly to the battery posts, via the battery switch terminals. At this point, THE PLOT THICKENS!!!
(a) - If the charger has a single output (or only one of its outputs is used) to charge both batteries, this would mean that the batteries are wired together on the charger. THIS IS WRONG! Check to make sure this is not the case.
(b) If the charger has two outputs, each connected to a single battery, that is the correct configuration. However, if there is a fault at the charger so that its outputs are not properly isolated from each other, one battery may discharge over the other via the charger.
(c) Of course, if any battery is connected to the output (i.e. common) terminal of the battery switch that is WRONG as doing so will result in wiring the batteries together depending upon the setting of the battery switch.

Long explanation, I hope it helps.


Good luck

[Gtown]

Yes, It needs to be switched to 1 or 2 to charge!
Also, the Carbon monoxide detectors are always on even if you have the battery switch on the OFF position

Thanks. Yes I realize the carbon monoxide detector, bilge pumps and mercathode all draw power no matter what setting the switch is on -- including the off setting. Still need to figure out what is draining the battery. Thanks for the info on the battery setting for charging. My challenge with this is if I'm away for an extended period of time from the boat I would like to disconnect from shore power. Hopefully the battery remains charged with the charger but if I turn off I'm back to having a dead battery.

[Gtown]

Actually if it was wired correctly the selection at the MBSS wouldn't matter. This schematic shows the general idea.

From memory this is how mine is configured. Bat is in storage now but will refer to this in the spring once the batteries go back in. Thanks.

[Gtown]

I did not know if you are/not connected to shore power. Leakage current corrosion occurs if you have two conductive paths; one through the water and the other (to complete the circuit) through the Ground conductor. If Mercathode does not detect leakage current it will not try to oppose it. I would still measure the current in/out each battery without the shore cable plugged in and also turn off the battery charger. If you do not measure any difference in current measurement and the current is very small very small, check the following;

1 - Make sure that the battery switch is indeed OFF
2 - Check the fridge(s); open the lid and check if the interior light is on. If the boat is wired correctly the fridge should not receive DC power when the battery switch is OFF
3 - CO detector should draw very little power. Do a test and unplug the CO detector when you leave the boat to see what will happen.
4 - If the bilge is dry, then the bilge pump is not a likely suspect.
5 - If, for some reason one of the batteries is bad, it may be drawing a lot of current from the other battery. If you have a battery isolator you should check if it is functioning properly and if its connections are good. If you have a bad isolator, one battery will discharge over the other.
6 - How the charger may affect things depends on how it is wired. As Bounty pointed out, if it is wired correctly, the battery switch position does not matter for the charger to charge the batteries. That is because, as his diagram shows, the charger is connected directly to the battery posts, via the battery switch terminals. At this point, THE PLOT THICKENS!!!
(a) - If the charger has a single output (or only one of its outputs is used) to charge both batteries, this would mean that the batteries are wired together on the charger. THIS IS WRONG! Check to make sure this is not the case.
(b) If the charger has two outputs, each connected to a single battery, that is the correct configuration. However, if there is a fault at the charger so that its outputs are not properly isolated from each other, one battery may discharge over the other via the charger.
(c) Of course, if any battery is connected to the output (i.e. common) terminal of the battery switch that is WRONG as doing so will result in wiring the batteries together depending upon the setting of the battery switch.

Long explanation, I hope it helps.


Good luck

Great explanation and some helpful tips on what to look for. A spring mystery to solve for sure once the boat comes out from storage. Thanks again.