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  #1  
Old 01-31-2008
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Question Battery Replacment advice

Hi everyone,

I have 2 battery banks, one side has 2 large golf cart batteries that work great, the other bank has 4 six volt deep cycle batteries and a 12 volt car battery all wired together. Over the last year, Ive noticed that the 6 volt side wouldnt hold charge but still cranks the starter fine...lights are dim in the cabin but good starts using that bank...I figured the 12 volt starting battery is good but the 6volts are bad, they are even bloated like they gained weight or blew up.. so my question is, should I keep this setup and replace the 4 six volts with some similar deep cycle batteries or should I get 4optima sealed blue top deep cycle batteries and rewire... also these batteries are under the rear quarter berth... maybe a sealed battery is safer on fumes when charging.....forgot to mention, this last summer I replaced my charger, I have a Pro-Tech i-series 1240i 40A capacity...

Last edited by peteramc; 01-31-2008 at 01:08 AM.
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Old 01-31-2008
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Your best bet is to get rid of the 6Volt batteries and replace them with equivalent deep cycle batteries of the 12V kind...It will make selecting a charger and maintaining your system much easier. Also perform a search on here, as batteries is a well covered topic

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Old 01-31-2008
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You need ONE starting battery and ONE bank of house batteries. If you mix different types and different "aged" batteries with new ones, you will shorten the life of the new ones.
If your starter battery is good...then it can be kept on "Battery 1" then you should build a new house bank of a size determined by your AMPHOUR needs and if you are not full time cruising, the batteries should probably be wet cells rather than sealed AGM's or GELs. You also need to consider your charging system (alternator and dockside) when designing your battery bank to make sure they are sized right for your needs.
Figure out your needs using the spreadsheet link here:
http://www.semarine.com/store/home.php?cat=87

Then come back and chat about what you should do and how to wire it all up. BTW...welcome!
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Old 01-31-2008
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Peteramc,

I agree with Comraderie that your system needs redesign and replacement of at least some of its components. Mixing battery types, voltages, and ages in the same bank is never a good idea. The fact that the 6V batts are distorting is a sign they're shot -- get rid of them before they start leaking.

It sounds like your 12V - 6V melange was intended as a house bank (lights, pumps, etc.) If so, you can replace it with either 12V or 6V batteries (with the 6V batts wired in series for 12 V output), but don't mix the voltages. House banks should be "deep cycle" batteries. If this is the bank you use primarily for starting the engine, then you can probably get by with a single 12V starter battery (some companies make a combo "starter-deep cycle" which is also an option).

A hint on buying replacement batteries -- don't buy them in a marine store. One advantage of wet cell (lead-acid) batteries is that they have wide industrial uses, golf carts and fork lifts being examples. Industrial users won't put up with the mark-ups we normally suffer at marina's boat store. Once you've redesigned the system and determined what you need, buy the batteries from an industrial supplier where the prices should be substantially less than the local West Marine (last time I bought batteries the price difference was over 30%).

You'll find that replacing batteries is a major investment. Read up on the topic -- although somewhat intimidating for those without an engineering degree, it's not rocket science. The keys to a good return on the investment are fairly simple: design the system properly, buy good batteries (Trojan offers very good value for money), and then take care of them. If you keep them clean, watered and fully charged when not in use, quality deep cycle batteries will last a long time. (Mine are 6 years old and may have another year or two in them).

You mentioned that you have two battery banks. While I agree with Comraderie that it's better to have one starter battery and one house battery bank, space considerations may make it impossible to physically put all the batteries together in the same bank. If the groups of batteries are not too far apart, they can be wired into a single bank, which is probably the best solution. If they are more than a few feet apart you may have to have separate banks. The problem in having separate banks (and for that matter mixing types, voltages and ages of batteries) is in how they accept a charge and how the voltage in the batteries registers with the voltage regualtor in the charging system (either the alternator or AC battery charger). Trying to charge two banks from a single charging source (or charging a mixed bag of batteries in a single bank) means that some of the batteries will probably get less than they need and remain chronically undercharged. This reduces both their utility and useful life.

Last point, I'd recommend you hire a marine electrician to help you with the installation of the new batteries. (You might also hire an electrician to help you with the redesign, or at least to check what you plan to do). While 12 V batteries won't kill you, they need to be treated with great respect. Getting the wiring wrong can be dangerous and might damage the batteries / chargers, etc. Unless you're supremely confident that you know what you're doing, fork over the $60-80 per hour you'll need to hire a good electrician.
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Old 01-31-2008
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Dispose of the 6v batts wired to the starting battery, don't change anything else until you follow Cam's advice, use the spread sheet to figure your needs.

If you decide to go with one bank, do NOT try and save money by putting new batteries in with your current batteries - all batteries in a bank need to be the same type and the same age. Not doing so will seriously degrade the life expectancy of your new batteries.

Save yourself a lot of time and money in the future by investing a few dollars and a couple hours each winter weekend to reading Nigel Calder and Don Casey; you don't own your boat until you can take it apart and put it back together again - better than it was.
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Having 1 bank split into 2 locations could lead to thermal runaway. There's a lot involved in setting up a battery system.

Calder's book on Maintainance & Repair goes into great depth on setting up battery banks for any application. Look up Calder on Amazon. It's a book every boat owner should own.
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Old 01-31-2008
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Quote:
Originally Posted by artbyjody View Post
Your best bet is to get rid of the 6Volt batteries and replace them with equivalent deep cycle batteries of the 12V kind...It will make selecting a charger and maintaining your system much easier. Also perform a search on here, as batteries is a well covered topic

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I'm interested to know why you recommend 12V over golf cart batteries.
The conventional wisdom seems to favor golf cart batteries for a number of reasons, among them being capacity/weight, ease of handling, flexibility, etc. What am I missing?
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Old 01-31-2008
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Quote:
Originally Posted by k1vsk View Post
Art
I'm interested to know why you recommend 12V over golf cart batteries.
The conventional wisdom seems to favor golf cart batteries for a number of reasons, among them being capacity/weight, ease of handling, flexibility, etc. What am I missing?
I don't pretend to speak for Jody - and seldom speak for myself

12v batteries have the inherent advantage of being the correct size for the built in battery boxes that most boat builders build for. There are signifigant modifications needed when upgrading/changing to a 6v system, the least of which is the cabling between the batteries. The extra weight, different, not yet standardized sizes can perhaps even cause structural modifications to adequately prevent the batteries from becoming missles.

Since the OP had questions at this level, it's often simpler to keep the recommendation simple.

I myself use 12v Blue Top Optima's because I can find a replacement anywhere, and they easily fit in the space provided without modification.
I lost a little total aH capacity, but not enough to justify the extra weight and mod's to my battery storage area.
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Quote:
Originally Posted by k1vsk View Post
Art
I'm interested to know why you recommend 12V over golf cart batteries.
The conventional wisdom seems to favor golf cart batteries for a number of reasons, among them being capacity/weight, ease of handling, flexibility, etc. What am I missing?
For a couple of reasons:

1. Simplicity of design and purchasing.

2. To have 12V you have to have 2 of the 6V and if you run them in parallel to increase amp hours achievable then that is four of them when only two of 12V would do. This means that at any given time if 1 fails - it immediately effects all other batteries rigged to ..that is 3 other batteries and trying to isolate whichever one is dead....kinda painful unless you enjoy doing that troubleshooting thing

3. The saving weight / additional amps is a myth... (see #4) the additional battery cables will often offset what supposed minimal gains you get from x more amp hours (but then most try to buy the cheapest not necessarily fitting to what ones boat requires)....

4. More corrosion of cables as there will be more cabling involved. and cables are not cheap often offsetting savings of purchasing two 6V versus a single 12V battery

5. Batteries are the core of the electrical system of a boat typically. The least amount of parts to make the system work saves in maintenance and troubleshooting time spent...

That is just the short list
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Last edited by artbyjody; 01-31-2008 at 11:38 AM.
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Old 01-31-2008
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Question

Quote:
Originally Posted by xort View Post
Having 1 bank split into 2 locations could lead to thermal runaway.
Could you explain this please.
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