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post #1 of 7 Old 05-23-2012 Thread Starter
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Battery Bank Confusion

Okay, so I have two batteries. Both are interstate batteries, brand new given to me by my old man, but one is a SRM-27 (750 MCA) and the other is a HD 24-DP (505 MCA). I have read the 12v Bible, which is a "Bible" without a doubt, and in it the author said to only bank batteries of like kind and and age. I am concerned if I bank these batteries for house use, I may damage one or both because they arent the same "size". I currently use the smaller one as a starter battery and the larger as a house battery. What should I do...buy another bigger one or another smaller one and bank the same size batteries? Is the small deep cell adequate to start a Yanmar 15hp? I am open to the masters of the electrical sea world to help me out here. The Yanmar by the way has a 35 amp charger which I plan to replace with a Balmar 70, and I am installing a 20 amp Prosport shore charger.
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post #2 of 7 Old 05-23-2012
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Battery Bank Confusion

By batteries of the same type they mean both should be wet cell, agm or gell. Size is less important. The deep cycle is generally used as the house battery because it can be discharged without being damaged.

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post #3 of 7 Old 05-23-2012
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Re: Battery Bank Confusion

In a perfect world...
But in this one, I'd say use the small one as a starting battery and meanwhile get a battery monitor, or a pencil and multimeter, and start out by checking your loads and needs and how far you can go with the existing batteries, bearing in mind that you don't want to draw the battery down more than 30-50% to get the best life from the battery.
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post #4 of 7 Old 05-23-2012 Thread Starter
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Re: Battery Bank Confusion

So buy another larger battery to give me a house bank of 200AH, and keep the small one as a starter? That makes sense. And if I "banked" a small battery and a big battery, I was under the assumption that this would be like trying to charge a "AAA" and a "D" cell flashlight battery at the same time, somthings not going to get charged properly....is this the right analogy? I figured type did mean wet cell or agm, but I also thought it might also include the "size" of batteries as well...but thanks for your help in understanding this, I think I will get another bigger battery....size does matter in some cases! Happy sailing!
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Re: Battery Bank Confusion

Don't buy anything until you've run the numbers (and monitor/meter) to find out how well your needs and battery sizing are matched.

Battery type usually means wet lead versus gel versus AGM, and you don't want to mix those. But Interstate also says your bigger battery is a "pure lead" design, which is still a bit rare and a little different from other wet lead batteries. Adding a twin might be a good idea--but might be a waste. You really want to run the numbers and figure out your energy budget before adding any equipment.
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post #6 of 7 Old 05-24-2012 Thread Starter
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Re: Battery Bank Confusion

Thanks HelloSailor for your input. Sage advice. Thats what I appreciate about this forum, non-judgemental, and kind, helpful encouragement. The group 27 batteries say there is 100Ah of power, and given 50% of this is 50Ah, thats only 5 amps for 10 hours. I have changed all my lighting to LED's which are a godsend power-wise. No refridgerator, no electric windlass, so I am skimpy on the power demands really. And other than leaving the VHF on and ipad/iphone charging, it's quite minimal. But for $100, another battery would be good investment in my mind. What did you mean by "pure lead" anyway being rare and different? This battery came recommended from the marina...
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Re: Battery Bank Confusion

The lead in batteries is usually of varying alloys for varying purposes. Sometimes to make it harder and keep it in place, sometimes because it is from recycled sources that aren't as pure. Odyssey has a line of "TPPL" thin plate pure lead batteries that are supposed to be outstanding because of the thin pure lead plates. Interstate says one of your batteries is from pure lead. I don't know anything else about it, just that they make that claim on their web site. Interstate arguably makes a good battery, you might want to ask them if there's anything special enough to "need" to match the battery with another of the same type, versus just shopping for a battery.

A VHF, squelched on receive, won't draw a lot of power. An iPhone can't be more than what, an 1800mA battery? That lasts 8-10 hours at least, so it shouldn't need more than 3 amps for a full recharge daily. If you can get 48 hours between battery charges without cycling it more than 50%, I'd say stick with what you have. When it is used up, then move to a bigger battery bank if you need to. If you can't wait but need more power now, then by all means, buy now.

The numbers will give you an answer.
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