Adding second battery; battery location

[zoom555]

Last summer I purchased a 1973 Northern 25. It had been kept in pretty good physical condition by the prior owner, but the electrical systems were pretty sub-par according to my surveyor. Mainly, the previous owner had cut corners. He used automotive or even household wire in some places instead of marine wire, household-style twist-on wire caps for connections instead of crimp connectors, etc. I dealt with those issues last year (replaced all the non-marine wiring and all of the offending connectors). My next challenge is to deal with the batteries.

The boat has a wood battery tray which is sized for a Group 31 battery. The battery is held down by a bungie cord secured to the wood battery tray. There's nothing to contain battery acid if the battery happened to leak. The battery is located in a locker under a settee. It is connected to a 6 amp charger (ProSport6). There's only the one battery. The engine is a 9.9hp outboard, so it doesn't require much juice to start.

I see several problems with the current setup:

1. The battery should be in a proper battery box to protect against spills. I'm planning to buy a Tempo brand box.

2. I'd like to have a second battery which would primarily be used as a back-up (I don't want to run out of juice for the VHF, running lights and GPS because we've been playing the radio for hours the night prior), but there isn't room in the locker under the settee seat for a second battery.

3. There may be an issue with accumulation of hydrogen from charging the battery in the current locker - it's an enclosed space. Last year I tried to just remember to take the cover off the locker after connecting to shore power, but it's not an ideal system.

So, here are the questions I'm hoping you folks can help me with:

1. Am I right to worry about ventilation? Any suggestions on how to deal with it? (If so, would a passive vent do? - something like the stainless locker vents I've seen for sale in marine hardware stores. Or, should there be a fan to blow air out of the compartment?).

2. Given the limited space available in the current under-seat locker, could I install my second battery in the comparable locker on the opposite settee? (This would require a battery cable run of about 8 feet once all the corners were rounded). The batteries would be electrically connected by a battery combiner for charging and otherwise separated and selected by switch.

3. Would I need a more powerful charger in this scenario?

I wish I had some photos to accompany this post, but the boat is covered up with tarps and for good measure, buried under the three feet of snow we've received here in the last week.

Thanks for any help that is offered!

[artbyjody]

Originally Posted by zoom555

1. Am I right to worry about ventilation? Any suggestions on how to deal with it? (If so, would a passive vent do? - something like the stainless locker vents I've seen for sale in marine hardware stores. Or, should there be a fan to blow air out of the compartment?).

Yes and no - the regs and standard practices say - ventilate... in most cases however - unless you have a really old battery (I doubt that)... or you have a charging system that cooks the batteries (very unlikely you play lotsa music and never was a problem)... the issue with ventilation really has to do with the proximity to to inboard gas tanks, propane systems and other gaseous and flammable mixtures...The regs tho rule - as they are designed for people without common sense in some cases...

Originally Posted by zoom555

2. Given the limited space available in the current under-seat locker, could I install my second battery in the comparable locker on the opposite settee? (This would require a battery cable run of about 8 feet once all the corners were rounded). The batteries would be electrically connected by a battery combiner for charging and otherwise separated and selected by switch.

Consider where you are locating the second battery. You will need a battery switcher (Perko or other) and the longer the run of main wire for batteries the more loss you get... BUT - if you place the batteries opposite or so and have the battery switcher in the middle - and for what you are trying to do - probably not an issue - although some that cruise and live off the batteries will give you very scientific reasons for doing this that or the other... (rightfully so if you have to be frugal)

Originally Posted by zoom555

3. Would I need a more powerful charger in this scenario?

Most likely yes, but they are around $120-220 bucks and probably worthwhile the investment especially if you go with gel or agm style batteries...If you do this replace the batteries with same make and brand (research batteries in the threads here I posted some input earlier in my life)...





I wish I had some photos to accompany this post, but the boat is covered up with tarps and for good measure, buried under the three feet of snow we've received here in the last week.

Thanks for any help that is offered![/quote]

[thekeip]

More important than ventilation is the requirement that the batteries be constrained to a movement of no more than 1" in any plane. That usually means a substantial battery box.
Howard Keiper

[sailingdog]

Originally Posted by zoom555

The boat has a wood battery tray which is sized for a Group 31 battery. The battery is held down by a bungie cord secured to the wood battery tray. There's nothing to contain battery acid if the battery happened to leak. The battery is located in a locker under a settee. It is connected to a 6 amp charger (ProSport6). There's only the one battery. The engine is a 9.9hp outboard, so it doesn't require much juice to start.

I see several problems with the current setup:

1. The battery should be in a proper battery box to protect against spills. I'm planning to buy a Tempo brand box.

You need to secure the battery box to prevent it from moving.

2. I'd like to have a second battery which would primarily be used as a back-up (I don't want to run out of juice for the VHF, running lights and GPS because we've been playing the radio for hours the night prior), but there isn't room in the locker under the settee seat for a second battery.

Try to keep the two batteries fairly close together. This will simplify wiring as well as charging them.

3. There may be an issue with accumulation of hydrogen from charging the battery in the current locker - it's an enclosed space. Last year I tried to just remember to take the cover off the locker after connecting to shore power, but it's not an ideal system.

Hydrogen is remarkably good at escaping any ventilated space. Put a small louver type vent in the side of the locker.

2. Given the limited space available in the current under-seat locker, could I install my second battery in the comparable locker on the opposite settee? (This would require a battery cable run of about 8 feet once all the corners were rounded). The batteries would be electrically connected by a battery combiner for charging and otherwise separated and selected by switch.

3. Would I need a more powerful charger in this scenario?

Closer would be better. If you could find a central location that would fit both batteries that might be even better, since it'd get the weight of the batteries down lower and that is always good.

Yes, a more powerful charger is probably a good idea. You probably want at least a 20 amp charger, since your battery bank will be about 200 amp-hours (100 or so per Group 31 battery), and the charger should be at least 10% of the battery capacity in amperage. A 40 amp charger would be better, since it would allow you to re-charge the batteries more easily, and the price difference isn't that big.

[zoom555]

Thanks folks - good suggestions all around. I'm not sure I'll be able to identify a better location for the batteries, but I'm going to take a look once the tarps are off in the spring. In the meantime, I'm collecting all the parts I need. I believe the battery boxes I was looking at come with a restraint device for the box, as well as something to screw them down internally, so I think movement should be well constrained once installed properly. It will work a lot better than the current wood tray and bungie cord arrangement, at the very least!

Thanks again.