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On several occasions here I’ve both recommended against and vented my angst with boatyards  that insist that batteries be removed for the winter to their customers. In my view this is simply a stupid, unnecessary move and it may even prove dangerous. Lugging heavy batteries up and down ladders once the boat is on the hard, the possibility of hooking the batteries up backwards (reversed polarity) in the spring rush, causing extensive potential damage to on board electronic equipment……this is just a partial list of why this historic procedure should be just that,,,historic.

Well anyhow I had an interesting conversation with a marine electrician from Wisconsin just before the holidays over this very topic. Keep in mind that for those of you that live in southern states, you have no idea of what cold feels like until you’ve been to Wisconsin in the winter. So, the people there are concerned about things like boat batteries freezing if they are left in a low state of charge during winter storage.

I’ve said consistently that if your batteries are left in the fall fully charged that the danger of them freezing during the winter lay-up period is non-existent. Well, to my surprise after talking with this tech, I may need to stand corrected!

According to this fellow, one of the boats he services each year is a 50 some ft. Sea Ray that he claims the parasitic electrical loads will drain down the battery(s) in a matter of a week.

Now, I am really quite surprised to hear this. Either the batteries are weak to begin with or the battery bank size is just plain inadequate. I’m finding it really hard to believe that the total parasitic loads, even on a 50 ft. boat, with undoubtedly tons of electrical toys with memory functions that may need power at all times could do this.

For those of you not following all of this keep in mind that discharged batteries can freeze and when they do they are destroyed. A fully charge battery will not freeze.

So, here’s what you need to do……. If you have happened to purchase one of the Blue Sea DVOM meters I have in my Ed’s Tool Box section of this site get it out. You need to set it up as shown here:


amp clamp

Next, get on the boat. Make sure the battery switch is turned off. Now clamp the meter around the positive battery cable with the + sign on the red clamp jaws aimed at the positive battery post. Turn the dial as shown above the the DC amps scale and take a read. Keep in mind that this meter is scaled down to hundredths of an amp, but it is not especially accurate at that low level. Accuracy is not that important here. You are simply trying to get a feel for the total of parasitic loads on your boat. For example in the photo above, the reading shown is 0.02 amps DC. That equates to 2/100 of an amp. Since there are 1000 milliamps in 1 amp of electrical current, this in turn equates to 20 milliamps of electrical current draw.

So, in light of the fact that many of your modern marine electronic toys are now specifying “zero-current draw” memory systems I’m suggesting that parasitic loads, even on a 50 some foot boat with all the toys is not too likely to have anywhere near 1000 milliamps of parasitic memory loads. Typical would be 25 mA or less and maybe as much as 100 mA at the most.

Check you own boat to be sure as explained above. If you do get a seemingly high reading on your meter, you need to carefully think out which of your on board electronic devices have a memory or digital clock integrated into them. Try to get some specifications on what the load is supposed to be and add them all up. It may well be that you could have enough of a draw to seriously discharge your boat’s battery capacity over the period of several months. I’d be surprised, but I’m not going to say its impossible any more in consideration of the vast amount of electical gadgetry a modern boat is likely to have.

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