Troubleshooting a drain on the battery

[Phlorida]

We took the boat out today and I had to jump the boat to get it to start. It has only been two weeks since I have been out and the battery switch was off. The batteries are one-year old Optima Blue Top Group 31's. Something is obviously pulling down the batteries.

I have recently upgraded the stereo and the GPS on the boat but I used the existing power leads and they turn off with the battery switch.

Does anyone have any guidance on troubleshooting this? It seems like if I use a multimeter on the circuit breakers I should see +12v on the offender(s) - does that logic make sense?

 

[Steve Craig]

All the breakers will show 12V when in the ON position, regardless of load. Many electronics will take a very minute current draw for internal memory systems.
With the battery switch OFF, you should see 0 voltage anywhere. ( Might be a by-pass for the memory set-ups but I'm not too familiar with boat systems.)
Even a new battery can have problems. Start with applying a load test. You can buy the tester or take it to a battery vendor for the test.
This will show you the general internal condition of the battery & it's abilities under load.
Next, put a voltage tester across the battery posts with the engine turning about 1500 RPM. Get some help if you're not comfortable doing this.
You should see +/- 14.4 V while charging. Tipping point I believe is about 13.8V, lower than that you may have a charging issue.

 

[JimG]

i have seen some radios memory draw a battery down when left for over 1-2 weeks. You might also make sure your bilge pump float switches are not stuck on.

 

[Phlorida]

Great advice Steve, thanks for taking the time. I had obviously presumed that one year old batteries weren't the issue and I will test them before I go any further. I guess that a standard 100A battery load tester will work on AGM batteries. The ammeter sure makes it appear that the charging system is working as expected but I will check that too.

All the breakers will show 12V when in the ON position, regardless of load. Many electronics will take a very minute current draw for internal memory systems.
With the battery switch OFF, you should see 0 voltage anywhere. ( Might be a by-pass for the memory set-ups but I'm not too familiar with boat systems.)
Even a new battery can have problems. Start with applying a load test. You can buy the tester or take it to a battery vendor for the test.
This will show you the general internal condition of the battery & it's abilities under load.
Next, put a voltage tester across the battery posts with the engine turning about 1500 RPM. Get some help if you're not comfortable doing this.
You should see +/- 14.4 V while charging. Tipping point I believe is about 13.8V, lower than that you may have a charging issue.

 

[Lazy Daze]

After verifying your batteries are good and that the alternator works, you can do an amp-draw test. Basically, this is to see how much current is being drawn off the batteries when the batteries are turned off. Remove the negative lead off the battery and hook your multimeter (on DC Amps) up between the lead and the battery. You should see a very miniscule amount of amps - probably less than an amp.

 

[Steve Craig]

I replaced mine last year just after purchasing the boat used. Two batteries, each of different manufacture & capacities. Load test showed one just over 11V & the other just below 10V, under load. Didn't trust them at all even before the test.
My alternator is charging +/- 13.3 V with engine under load at about 2000RPM. Not too comfortable with this either. I have a new alternator to put on in the Spring. I'll rebuild the old original & have a spare. DIY rebuilds are very simple once you get everything cleaned up.

Dennis,
Will a battery switch open the circuit to the bilge pump or will it remain energized with a separate direct line?

 

[Phlorida]

Thanks again. The way that my electrical system is designed is that there is a circuit breaker box in the engine room with circuit breakers for "bilge pump," "sump pump," and "console." There are two leads that come from the circuit breaker box to the battery switch that should be for the bilge pump and the sump pump.

 

[Phlorida]

My experience was similar and I replaced the batteries with Group 31 Optima's almost exactly one year ago. I haven't had issues with discharged batteries until recently. I haven't checked the charging voltage and will do that this week.

I replaced mine last year just after purchasing the boat used. Two batteries, each of different manufacture & capacities. Load test showed one just over 11V & the other just below 10V, under load. Didn't trust them at all even before the test.
My alternator is charging +/- 13.3 V with engine under load at about 2000RPM. Not too comfortable with this either. I have a new alternator to put on in the Spring. I'll rebuild the old original & have a spare. DIY rebuilds are very simple once you get everything cleaned up.

Dennis,
Will a battery switch open the circuit to the bilge pump or will it remain energized with a separate direct line?

 

[mawyatt]

After verifying your batteries are good and that the alternator works, you can do an amp-draw test. Basically, this is to see how much current is being drawn off the batteries when the batteries are turned off. Remove the negative lead off the battery and hook your multimeter (on ohms) up between the lead and the battery. You should a very miniscule amount of amps - probably less than an amp.

Dennis,

No....no!!!! I hope you mean on DC amps....not Ohms!!!!! . Usually you will need to move the + lead on the multimeter to another indicated slot (done for safety reasons). Do not try and start motor or anthing like that as this will most likely blow the fuse in the multimeter. Please remember to return + meter lead to the normal slot.

 

[Lazy Daze]

Dennis,

No....no!!!! I hope you mean on DC amps....not Ohms!!!!! . Usually you will need to move the + lead on the multimeter to another indicated slot (done for safety reasons). Do not try and start motor or anthing like that as this will most likely blow the fuse in the multimeter. Please remember to return + meter lead to the normal slot.

YES! Thank you for catching me on that, Mike. If any voltage is applied to a multimeter while in the "ohms" setting, it will (at least) blow the fuse. Ohms can ONLY be checked with no voltage present.

Thanks again for catching me on that. I'll edit my original post for clarity's sake.

 

[Lazy Daze]

Dennis,
Will a battery switch open the circuit to the bilge pump or will it remain energized with a separate direct line?

While I'm not 100% positive on how thing were setup on early boats (say, '80's and before, for example), the "normal" way that things are hooked up are...

When the battery switch is off, certain things still require power and are wired "around" the switch. These would be: Bilge pump, Engine Computer (if it has one), Radio Memory (for the radios that have that feature, which is pretty much all digital radios) and CO detector (again, if you have one - which you should if you have a cabin).

Even with all (4) of those things, an engine can sit for 2 weeks and should start up just like it was only sitting for a day. IF not, something else is going on.

 

[Phlorida]

No engine computer or CO detector on my boat. It is designed for at least the bilge and sump pump to operate with the battery switch off although I notice that a few other things work also. I used the memory power wire on my installation which is hot with the batteries turned off.

I was thinking the same thing about two weeks of sitting idle with two newish group 31 AGM batteries. I am going to buy a load tester and swing by the boat tomorrow. I'll also check for a draw on the engine.

Thanks again for everyone's insight and support.

While I'm not 100% positive on how thing were setup on early boats (say, '80's and before, for example), the "normal" way that things are hooked up are...

When the battery switch is off, certain things still require power and are wired "around" the switch. These would be: Bilge pump, Engine Computer (if it has one), Radio Memory (for the radios that have that feature, which is pretty much all digital radios) and CO detector (again, if you have one - which you should if you have a cabin).

Even with all (4) of those things, an engine can sit for 2 weeks and should start up just like it was only sitting for a day. IF not, something else is going on.

 

[Lazy Daze]

although I notice that a few other things work also.

There's always that "what did a prior owner do" factor to contend with... :smt101

 

[CV-23]

I'm also having the same issue,,,,,trim pump is also wired before the Perko switch. I get a small spark hooking up my starting battery with the Perko switch off. I also have the house battery still out of the boat. What about the Mercathoid System running? I know my bilge pumps are not running......tested them, Mike.

 

[Lazy Daze]

What about the Mercathoid System running?

Hmmm. Never seen that before. But you probably should hurry up and go catch it. :grin:

Yes, you're correct - the Mercathode is hot regardless of battery switch. Trim switch should not be drawing any power unless the switch is pressed.

You can get inexpensive DMM's for under $10 that will be plenty adequate for this purpose.

 

[CV-23]

Yea....my son has one. I'll have him check it at Easter when he's home. Can't imagine where the draw is coming from other than my Alpine Radio memory and it can't take that much, Mike.

 

[CV-23]

My house battery seems to be charging fine in the garage/charger. It was drawing 10amps when I first started charging it in the boat and kept tripping my converter breaker in the boat. It's a 30 amp Pro mariner charger and the Boat breaker can't handle it I guess.....seems odd. It's charging the starting battery just fine. I pulled the house battery so I wouldn't hurt anything and I'll get it tested later this week. Both batteries came with the boat and are 2007 date code....probably need new ones soon, Mike.

 

[CliffA]

i'll offer a suggestion about tracing down a power draw from a battery, but i will admit up front that electrical issues and trouble shooting are not my strong suite....i have not used this process but it seems like it should work...others with more electrical knowledge than me will chime in if this is not correct....turn everything off and measure the voltage across the pos and neg battery terminals with a voltmeter....then pull a fuse from the fuse box...recheck the battery voltage...if the circuit that was controlled by that fuse was causing the power draw you should see a slight increase in the battery voltage once the fuse for that circuit was pulled...if there was no change in the battery voltage replace that fuse and pull the next fuse in the box and retest the battery voltage....continue this process until you discover which circuit is responsible for the power draw on the battery...then you can check each component in that circuit one by one and the associated wiring to locate the source of the problem...

cliff

 

[Jimmy Buoy]

Testing for power draw using the + and - posts and the resulting voltage reading will not give you the answer you need. What WILL give you readings for the amount of power being drained from the battery has been mentioned in post #5 (Dennis). It involves disconecting one of the battery's posts and placing an Amperage Meter "in line" between the empty post and the disconnected wire. The meter will show the number of Amps being used. Zero amps = no drain of the battery. If the drain is higher than an amp, start disabling breakers/fuses and see the affects on the Amp total.

Refer to the previous post for details and do not use the OHM setting for this - it will damage your meter!

Ever seen Apollo 13 with Tom Hanks??

 

[CliffA]

Testing for power draw using the + and - posts and the resulting voltage reading will not give you the answer you need. What WILL give you readings for the amount of power being drained from the battery has been mentioned in previous posts. It involves disconecting one of the battery's posts and placing an Amperage Meter "in line" between the empty post and the disconnected wire. The meter will show the number of Amps being used. Zero amps = no drain of the battery. If the drain is higher than a couple of amps, then start disabling breakers/fuses and see the affects on the Amp total.

Refer to the previous post for details and do not use the OHM setting for this - it will damage your meter!

thanks for the correction Jim....