Battery Drain

[daniel123]

I have a new Humminbird Digital three-stage on-board charger and it's attached directly, one to a deep-cycle and another to a starting battery aboard my Osprey. The third stage is not hooked to a battery as this point and is capped off. The batteries are connected to the boat's electrical system via a common Rule three-way battery selector switch, which is wired to give me the option of using Battery 1 (starting) or Battery 2 (deep cycle) or Both batteries when needed by switching the Both, or no batteries when switched to Off, to save accidental discharge.

I leave the switch in the Off position while the boat is stored on the trailer, often for weeks or months at a time, but still have to plug in the charger to recharge the batteries once a month or so to bring them from an average of 25% back up to 100% charge. I believe the only direct wire connection that isn't going through the selector switch is from the starting battery to the auto bilge pump switch, so that it works automatically when the boat is at a dock even with the bilge pump dash switch off and the battery selector in the Off position.

I can see how that may drain that one battery when it rains and the pump cycles on and off to discharge rainwater collecting in the bilge. But why would both batteries drop to as low as 25% charge when they are connected to the switch when it is in the Off position and there is no apparent drain on them?   

[Capt. Bob]

Flooded lead/acid batteries?

How old?

[daniel123]

Sorry, Bob. I thought I was signed up for alerts whenever I got a reply to my posts and didn't see this until I logged back on just now. Flooded lead acid, two and three years old.

[Keith Knecht]

I'm sure Capt Bob will chime with the appropriate documentation but your batteries are like me, old.  Three years is my general rule of thumb for replacing batteries.  Do they last longer, yes, but it sounds to me like yours are on the way out.  I have been known to be wrong.

[daniel123]

Perhaps you are right, and we have a family vacation trip coming up this Xmas when we use the boat to get to and from our destination (North Captiva Island, FL) as well as using it to fish daily for the week, so new batteries probably make sense regardless. Is there a consensus on what type of batteries to replace them with these days? I use the deep cycle primarily for a 12 volt, 55-lb-thrust bow-mount motor that doesn't see extended use and as a back-up for starting the 1999 115 Johnson Two Stroke that can take some cranking when it hasn't been started in a while. Perhaps I should replace the pair with two deep-cycles, since new batteries available today have the capability to handle both starting and deep-cycle duties? And I'm interested to learn what CAS members recommend with regard to lead acid, gel or AGM batteries in such applications. Thanks in advance for any input.

[Blue Agave]

I've had great success with AGM batteries. I find the link below to be informative.

http://www.dekabatteries.com/assets/base/0406MarineApplicationslayout.pdf

[Capt. Bob]

My reason for asking was explained by Keith. They are on a downside for this type battery with the style use they get. When placed in a vehicle (say a car) that gets daily (or several times weekly) use, and has a sound charging system, they are maintained fairly well. They rather enjoy this life and like some humans that take care of themselves, they are rewarded with a little longer life. Most boaters don't maintain their batteries in that manner and so the flooded type don't seem to have an extended life.

I started using Gel types in 1998. They have good and bad characteristics (like a lot of us). They don't seem to supply the same cranking power per group size as the flooded/AGM and they can be picky about how they are charged. Still, mine have lasted many years but......

Replacement costs are absurd and since I'm running a primitive charging system on my old Yammy, I replaced one (yes I still run one gel) with an AGM. The thought is (when the time comes) to replace the other gel with an AGM too. I also up-sized from a Group 27 to 31 (fits in the same size battery box but heavier) and love the extra bump in cranking amps. I won't go into the differences (BA's link is your source) but the AGMs seem to give you the best of both the old school (not too picky about older outboard charging systems) with the extended intervals in charging maintenance when your boat sits. The manufacturers appear to have worked out the bugs early models had and the costs are palatable. I would suggest you take a good look at the AGM type for replacement. Deals are happening more often than not so shop around.

Good luck.

[daniel123]

Menard's has the Exide Marine Group 24M AGM (FP AGM24DP) on sale for $150 right now -- less another 11% through Saturday. The cheapest I found them on Amazon was $225 and they are highly rated by what I learned on line. They are Group 24s, which the Deka chart shows is the "Best Fit," but I'm thinking Group 27s (31s?) might be better? I'm going to buy two of whatever I get so that I start out with two equal cells. Thoughts?   

[RickK]

If you are a member of Sams Club check them out.  I just bought a 27 agm starting for I think $80 with a 12 month warranty.  It used to be that Sams carried a few different batts, now they have a ton of them, at least in the one I shop.  Lots of golf cart batts.

[Capt. Bob]

As for the type, well you need to know how you use your batteries.
I'm old old school in that I use one (hopefully) battery per trip, then switching to the other on the next trip so both of mine are dual purpose/deep cycle types. This was common practice years ago when sophisticated electronics consisted of a VHF and a flasher for depth recording. While I realize I'm in a minority who still use this method, it continues to work for me. Electronics today are very hi-tech and tend to not like spikes (or under voltage) to their systems so you might think of additional ways to protect yourself since you mentioned a new device on your boat.

My older stuff seems to work fine the way I have it wired but that might not be the best thing moving forward.

Good luck.

[daniel123]

I'll check out Sam's Club, as I have a friend who is a member. Meanwhile, are 27 series that different/better than the 24 series my outboard is rated for?   

[Capt. Bob]

are 27 series that different/better than the 24 series my outboard is rated for?   

From a construction standpoint material wise no but...

27s are a little bigger and use a different tray/box to mount. They do weigh more and will often (but not always) have an increase in cranking power and reserve. Again, you need to compare the two to make the best decision. You may find a higher grade 24 that exceeds a lesser grade 27 in that respect.

 I always ran 24s in my 17 with a 115 Johnson and never had problems but as I stated earlier, not a bunch of electronics. I switched to 27s when I up-sized to a CCP with a 200 Evinrude and ran 27s on my 200 Yam. I went to a 31 (which is heavier still) because the price was right and I gained extra cranking power and more reserve than my old gel (yet fit in the 27 box). Nowadays a little extra reserve power with all the electronics you may want to run (including pumps)and additional cranking juice, if the price is right, is the way to go.

You know best how you run your boat so base your choice on that factor, not so much on "bigger is better".

Good luck.

[daniel123]

Thanks, Bob. I may go straight to a pair of group 31 AGMs and use them both for starting and deep cycle use, alternating their use via the battery selector switch. Does that sound like a good plan? I run a 12 volt 55-lb thrust MinnKota on the bow, but not much, and have never drained the single group 24 flooded cell deep cycle I have been using to power it. I figure a Group 31 deep cycle AGM will be an improvement in that regard. The only issue is if I start to use the bow-mount more, and I decide to use a second Group 31 wired to double the 12 volt deep cycle power and whether it will fit under the Opsrey's console with the other two 31s. The only other issue I have is that I have read that AGMs may not recharge to full strength if allowed to drain to less than 50% charge, which will likely  happen in my case since I'm only using one. Is that an issue?

[Capt. Bob]

OK,
As stated before, I've experienced no noticeable problems running my boat in this manner. My electronics (sounder, GPS and VHF) have suffered no problems. Newer electronics might not be as forgiving, I just don't know.

Group 31s will be heavier. Remember that when hauling them around.

I have found that AGMs will recharge at percents less than 50. The key is the right battery charger. My current AGM was accidentally left on for several weeks and was drained down to less than 4 volts IIRC. I tried recharging with the multi-stage charger I had used for years but with no luck. The charging algorithms in that older charger couldn't sense the lower voltage and failed to initiate a charging sequence. I bought a new charger that does and it (AGM) came right back to life. Baring a mistake like that or the possibility of it happening say with a stuck bilge pump float, I think you'll find that they hold a charge much longer than even a new flooded type battery. I began charging both my gel and AGM batteries last Friday. Both had been fully charged in May and both showed 75% remaining when I began. They have not had any additional use, other than starting the motor on the muffs twice. and running for a short period of time. No, I don't get out much any more.

That stated, I would not worry about the batteries dropping below 50% charge. Regular maintenance with a good smart charger will prevent that and you'll be fine. They are very forgiving in my experience.

[daniel123]

Thanks for the advice, Bob. I just installed a new MinnKota MK-330 Digital 3 bank/10 amp on-board charger that offers an AGM charging option. I assume that has the capability to bring back AGMs that have been deeply discharged. That would be the only charger I'd use to maintain the batteries, other than the charging system on my 1999 Johnson 115 Two Stroke. Any issues with the latter working to charge an AGM? And when I put the Rule battery selector on "Both" while running, it should re-charge both batteries while underway, correct?