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Old 10-26-2012, 03:10 PM   #1
CLV
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Default DUAL BATTERY SWITCH operation on 2008 2100sc3

Hi all

I have just had to replace the battery for the second time on my 2100Sc3. Its the same as before, being the battery behind the other one.

The dealer has told me that by running the boat with the battery switch on both that it does not charge both batteries so should start and run on alternate batteries settings on alternate outings. I only go out for the day before its trailered home.

They have also told me that Maxum wire them up such that there is always a live feed even with switch in the off position to retain power to the two bilge pumps and the radio memory and over the winter period when the boat is not used this has drawn the power down from that battery and killed it. It was new two seasons ago. That seems really strange to me. Does any one know for certain if that is true? Thanks!
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Old 10-26-2012, 04:27 PM   #2
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CLV,

I would disagree with the dealer; running with the switch in the "Both", or 1+2 - however the switch is labled, position should indeed charge both batteries. If you can get to the batteries (they were miserable to get to on my 2400 SC3 - so I moved them) you can verify by using a multimeter to measure voltage at the battery terminals with the engine running (either in the water or using muffs). With the engine off check both batteries - each should be right around 12V. Switch to Bat 1, start the engine, check voltage at Bat 1 - should be upwards high 13 or low 14. Switch to Bat 2 - should again be 13/14. Switch to Both and check both - should also be 13/14.

The second point is probably true, and is on mine. If you look at your batteries you'll see, in addition to the thick main cables, some smaller wires connected directly to the battery. Anything connected directly to the battery will not be controlled by the battery switch. However, since you the boat is not stored in the water the pumps won't ever run (unless you store it uncovered and it fills with rain water). The radio memory draws very little power, as does the CM detector in the cabin.

During the season it isn't uncommon for my boat to go unused for over a month (a darn shame, that) and the battery is never dead. During the off season I remove both batts and store them in my garage and maintain them on a trickle charger. Since you take your boat home with you perhaps a trickle charger would be a good idea for you too.

Dan
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Old 10-26-2012, 04:53 PM   #3
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Thanks for your reply Dan. I have owned big boats (40') before with proper house/start battery arrangement so can't quite figure out the set up on the maxum 2100 and if now I should run on alternate switch settings. Personally I would have thought that you run on "both" until you get to anchorage then switch to one or the other to run "house" if you are there overnight for example, then know you have a reserve charged battery just in case. What may be of interest though is that the boat starts no problem in 1+2 but the rear battery is in fact dead and the only way we found this out was when I asked the dealer to give the batteries a bench charge while in for its service so its only the rear battery that isnt being charged and that was a brand new battery two seasons ago. The dealer said that if the one battery is low then the alternator doesnt see a low charge because of the good battery voltage.
I think the cm detector has an internal rechargable battery as it will go off a while after the battery switch is set to "off".
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Old 10-26-2012, 07:27 PM   #4
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Ah, then you know your way around boats, CLV.

Your dealer's comment: "if the one battery is low then the alternator doesnt see a low charge because of the good battery voltage". I don't think that is correct. When 12v batteries are wired in parallel they become one big battery but still supply only 12V to the load(s), and it doesn't matter how many there are. However, when one battery is fully charged and the other is discharged then turning the switch to both will cause both batteries to be less than 12V. In otherwords, if one is at 10V and the other at 12V you end up with one big battery at 11V. From what I've read it doesn't happen instantaneously, but how long it takes depends on how discharged the one battery is. Voltage from the charged battery flows into the discharged battery. Regardless, The engine's alternator still only "sees" one battery and is going to charge it.

I make my "which to run on" decision based on a few things, like how long has it been since I used the boat and, therefore, the relative state of charge for each of my two batteries.

I have 1 regular lead acid battery (Batt 1) which is generally my start battery, and one AGM (Batt 2). AGM's don't discharge from non use as quickly as LA's do. I start up on B1/lead acid and run to whereever I happen to be going to get it charged back up. Drop anchor/tie up and switch to B2 (AGM). Back to B1 to re-start, then switch to Both for the run back to the marina. Or, if my run to where ever will take an hour or more I run for about 30 minutes on B1 then switch to both.

The first season with the boat I had only the lead acid battery - which was installed new when we bought the boat. I installed the switch and the AGM in the spring of season 2 and have been operating the boat as discribed above for 3 seasons, which makes the LA battery 4 years old and the AGM 3 years old.

Dan
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