Starting battery draining

[mphem]

I have a 2003 43DS and my starting battery is draining down. Has anyone had this same problem and can offer any suggestions? My boat is currently on a nearby fresh water lake and we go up most weekends and never less than every couple of week. I first noticed the problem a couple of months after I purchased the boat in June 2013. The first time I simply replaced the battery, not knowing the age and believing it was bad. I later found out that the previous owner had replaced it, not long before I purchased the boat and he knew something was pulling down the battery, but did not tell me. Since I replaced the battery, it has gone down a couple of additional times and was down again this weekend. I have noticed that it usually has about 5 volts remaining, but that may just be when I am noticing it. I purchased a battery charger and it will charge in a couple of hours to the point I can start the boat and then will get fully charged from the alternator and is good for another couple of weeks. It is my understanding (from the previous owner) that the starting battery only recharge from the alternator and not from the shore power/generator charger. I also heard from the forum that I should alway turn the windlass switch (located in the aft cabin) off, as that could be the source of my battery draining. I did turn it off, but that didn't solve my problem. Again I'm not sure, but I believe the windlass operates off the starting battery and because of that I have never run the windlass without the engine running. Also I have a question regarding the battery switches located in the aft cabin. I currently leave all the switches on, including the ground (I have been told never to turn the ground off, unless all the positives have been turned off first), house batteries and starting battery. I have assumed that since we are at the boat on a regular basis and we keep food in the refrigerator/freezer that I need my house batteries (lights if I arrive at night, etc). My question pertains to the starting battery. Should I be turning it off, when I leave the boat and if so would not turning the battery off be somehow connected to my drainage problem?

Again, any advice would be appreciated.

Mike

[Don Reaves]

Diagnosing a problem like this is a process of elimination. You need to find out what's draining your starting battery, and the refrigerator is the first thing I would look at. Does it still run when you turn off the main positive switch for the house battery? I wouldn't expect it to, but if it does, that's probably it.

I would turn off the main positive switch for the starting battery when leaving the boat. If it still discharges, then there must be something connected to the battery that bypasses this switch. And if that's the case, I would want to find out why. If it's not justified, it should be rewired to go through the main switch.

Actually, my first inclination would be to trace the wires to find out what's connected to the battery, but just turning off the main positive switch is an easy first thing to try.

Don

[sitara]

I had a faulty battery isolator on my SO36i which effectively resulted on one battery bank, so that both the house and the start battery discharged through the house circuits. This showed up as falling start battery voltage even when the main isolator switch to the start battery was off. Also a wiring fault allowed the start battery to discharge through the house circuits when the house battery isolating switch was off!

I always turn the start battery off when leaving the boat, my boat has a keyless start system that is active if the house battery is on.

[windward54]

I also had a bad battery isolator, and that was the first thing that came to mind. The isolator was a Newmar and was causing a voltage drop across the device. The device was also generating a lot of heat, especially when the battery charger was running. Because of the voltage drop, the starter battery was never getting charged. I replaced the unit with a Blue Sea Combiner and all worked fine.

[pbunning]

I agree with Don. You need to understand exactly what is connected to the battery. I usually keep the engine battery isolated whenever I am not using the engine or sailing. Only connections in this condition should be from the mains battery charger (if connected) and possibly from diode splitter (if used).

[Xlnt]

Same problem on my boat, the isolator connected all batteries together, so when draining the house bank I automatically drained the start and aux bank as well. r\Replaced the isolater with one from Quick and all well since.

-Xlnt

[electricmonk]

These problems are often a devil to solve, first thing I would do is try and ascertain what modifications have been made to the electrical system.

Your shore power charger does not sound like the standard fitting - needs investigation.


This is a flyer: a could be or a maybe

Has the standard splitter diode been removed and replaced with a battery combiner? if yes what did they do with wire labelled "ALT2"? if they connected it to A battery positive (to sense the battery voltage - a logical thing to do but see below) then that would drain A battery very slowly (through the alternator) depending on how the combiner is fitted (priority to the domestic bank or priority to the starter bank). - sounds like priority to the starter bank and it's sensing the starter battery ALL THE TIME.

ALT2 is not required for a battery combiner (VSR), the voltage is sensed via ALT1 which is already connected to the alternator via the key switch, connecting ALT2 bi-passes the key-switch and permanently drains the starter battery very slowly. ALT2 is ONLY required for splitter diode systems and the Hitachi style alternator.

(The topic this week on Electric Monk has been whether to fit a battery combiner or not - I think I've identified all the problems . . . famous last words)

IF what I have said above is so, then it makes perfect sense that a simple single output battery charger connected to the domestic bank would never charge the starter battery as the combiner will always be disconnected waiting for some volts from the alternator, volts which will never come because the starter battery is flat!

QED

[coffsguy]

I had a recent conversation with a marine electrician who mentioned that in some boats the alternator/charger charges the house batteries first then the crank battery. Perhaps if your house batteries are not fully charged first then this may be the cause of your problem.

In any case installing a crossover switch so you can use the house batteries to crank your motor would be a prudent decision.