batteries

[billyb]

That is a whole thread on batteries. I use AGM batteries, but just a good deep cycle works fine, you just have to be able to get to them to check fluid levels and condition routinely. Shipping a battery is a big cost, so finding one locally will end up being cheaper. Depending on your desire, a group 31 offers the most amp/hour capacity, and a group 27 is next, followed by your stock group 24 battery. I pulled out my stock group 24 in the Nauti Dawg, and installed two group 24 batteries, and never lacked for power combined with a Blue Sea Switch and ACR. But when you combine batteries, they need to be like size and condition. So adding a group 31, that will combine with an ACR when charging, isn't a good idea with your stock group 24. Because the bigger will have more amps to flow to the smaller when they are pretty full, and when drained, the condition is just too far different. Keeping them the same is important if you combine them. But you could just use a big group 31 or 27 for stereo, and keep the group 24 for a start battery, and not use an ACR. Up to you...

This is the first time someone has explained this and had it made sense to me, THANKS.

 

[David Analog]

Mel,
Are you recommending to stay with symmetrical battery sizes on separate battery banks when using an ACR?

 

[txav8r]

Yes David, and same condition as well, meaning age. I think you and I have discussed that maybe brand isn't that important, but if they are not similar amp/hour, size, and construction, one battery could dominate the other. It is a big no no in series, but it just isn't a good idea in parallel either. Because an older or smaller battery will not get the same treatment as the newer or larger when charging, and the older/smaller could end up sulfated. Now, if you have dual charging on shore power, you may avoid all of that, and just use the ACR for supplement on the water. But the reality is that we have guys that don't shore charge...ever, and battery condition is questionable. That is certainly going to not let the larger, more expensive bank get fully topped off. That will gradually degrade that bank. So keeping everything equal is even more important. I am not saying you can't do it, I am just saying that unless you maintain them both on and off the water optimally, you may find yourself spending more money than you have to. I used one pulse tech on my batteries for several years, with an ACR allowing shore power to charge both banks at home. That too is a bad idea, even though it works. Because the smart charger is not only a charger, but it is optimized for polarity as well as battery condition. It may never see that one battery is bad if it sees a good battery between the two of them...and then it can and will charge a bad battery. I won't do that again, and will use a dual bank charger at home on my two battery banks.

 

[David Analog]

I agree and we are pretty much on the same page. In my own words....
I do not believe there is ever a scenario when it would be acceptable to have anything but identical batteries in parallel or series on the same bank.
I think any system in a boat or car, charged by alternator, stator or shore charger, where multiple banks are charged by a single charging source is automatically flawed. And we have to live with those little conflicts.
Even identical batteries on different banks will often be discharged and recharged differently and can not remain identical for very long under those circumstances. Eventually the dual banks, whether using an ACR or manual switch, are likely to be combined at some point and there will be a small charging inequity based on batteries with different internal impedances.
I agree that if using a common single bank charger on both battery banks that you would want to lean towards similar batteries.
And I would likely attach the single bank charger to the battery or bank that routinely gets discharged the deepest.
Keep in mind that different batteries with very different reserve capacities will not pass current between them until there is a voltage differential. A difference in voltage potential is the only impetus for current flow. And that the presence of an active alternator can also influence the flow of current so that any rapid correction may not be as volatile. If I have two asymmetrical banks with separate shore charger banks servicing each bank then I am not concerned. I kind of throw that into the bag with all the other charging system imperfections. And I sleep very well.

 

[MOA_Chaser]

I bought the biggest DieHard marine AGM a couple years ago when it was on sale and haven't had any issues, and haven't come close to running it down. I have a smaller multipurpose marine battery as well, they're on a 1/2/1+2 switch which is never put to 1+2. I use a Guest dual bank charger that charges each battery individually.

 

[Seadeals]

I have two group 24 batteries on a BEP 1/2/1+2/off switch. Both batteries were used when I got them. One is a 2008 Deka and the other a 2011 from Costco. I use one battery on the water with a second just as a reserve. I thought about replacing both a few years back; but once I got a BatteryMinder 1500 and hooked it up when I put the boat away, both have been acting like absolute rock stars for two seasons. I alternate use and take voltage readings after each outing.

I recently forgot to switch the selector to off and had switched the minder to top the other battery (stupid user error). The Deka drained to 1.5v. It actually recovered; but I am figuring it is on borrowed time now. With the other being cheaper and still "old" I plan to buy a matched pair in another month or two.

I went with an Optima yellow top for my truck since my Minder works with Optimas and I am thinking a pair of blue tops for the boat ($$$ to buy batteries AND a charger). If I have two new matched batteries, are there any risks to using the (1+2) to exercise both to a shallower drain aside from having no backup if I run them both down?

 

[David Analog]

I'm not sure I fully understand but I'll take a scattershoot at answering.
When we use the term 'exercise' we normally mean to excite the battery chemistry via enough current as to counter the effects of sulphation....specifically when recharging with a shore charger.
I would never advocate using both batteries without keeping one battery isolated in reserve.
If you are discharging a single battery too deep (below 11.8 to 12.0 volts) then you do not have enough battery for your application.
A 1.5 amp charger is great for maintenance when the battery is placed into storage already at a full charge. But it is not enough to 'exercise' the battery when deeply discharged.
I would use a smart dual-bank three-phase charger in the following class:
2 X 10 amps for two group 34 or 24.
2 X 12 amps for two group 27.
2 X 15 amps for two group 31.
Or a charger amperage capacity of 10 to 13% of the battery's amp/hour rating.
I like the scheme of having two identical batteries and alternating their role weekend to weekend. This will prolong the life of both batteries by limiting their number of deep cycles and balancing their status relative to each other. If I had a single bank charger then I would alternate its use according to the battery that was deeply discharged. However, as stated above I would change to the appropriate dual-bank charger if my discharge cycles were deep.
It's great that you actually measure voltage at key times rather than leave the status to speculation.

Quote;
"I recently forgot to switch the selector to off and had switched the minder to top the other battery (stupid user error). The Deka drained to 1.5v."
You lost me on exactly how your actions led to this outcome. Was there some sort of parasitic drain?

 

[Seadeals]

Thank you @David Analog. While working winter mods, I often enjoy the boat's stereo. I also usually swap the minder from one batt to the other to keep things fair. I had done both and briefly used the radio to draw off the top charge for an accurate volt reading. Then I got distracted and never turned the batt switch off. Then it saw a few weeks of parasitic drain. After outings, the used battery would still often be at 12.8, so I have apparently never scratched the surface power draw or the need to hook up my sears lead acid charger. If I get new optimas or other AGMs, point taken, I will definitely need to get a good charger too.

 

[bthessel]

View media item 2271So here is what I am thinking for my battery setup. If I keep the 24 AGM for starting and get a 27 or 31 AGM for house. I would wire them like the diagram below, realizing that when the 4 way switch is set to 1 only the starting battery will charge while running. If the starting ever fails I can switch to 2 or both to get going. I have a ProSport12 dual bank charger I will mount next to the batteries to charge them both every night when the boat is pulled out of the water. Does anyone see a problem with this setup I am not seeing?