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Author Topic:   Battery For Electronics
mrtoyz posted 06-19-2010 11:40 PM ET (US)   Profile for mrtoyz   Send Email to mrtoyz  
Current battery [is a] Interstate Marine Starting Group-24. Should I be looking at a larger battery or possibly two batteries for the following items: Lowrance Sounder, Finder and GPS combination instrument, portable VHF charging stand, [audio entertainment device with four] speakers (which will be running quite often when the engine is off)

[What is the] minumum [battery rating in] Ampere-hours?

David Pendleton posted 06-20-2010 08:46 AM ET (US)     Profile for David Pendleton  Send Email to David Pendleton     
You shouldn't run electronics (or anything else that places a continuous draw) on a starting battery. You should have a deep-cycle battery with the highest Ampere-hour rating you can find and afford. You should also run both batteries through a battery switch. Use your starting battery to start your engine(s), and the deep-cycle battery to power electronics.
jimh posted 06-21-2010 10:21 AM ET (US)     Profile for jimh  Send Email to jimh     
We cannot know the minimum Ampere-hour rating for a battery to run the equipment you have listed until you tell us the current drain of those devices and the length of time you plan to have them operating from the battery.

A starting, lighting, and ignition (SLI) battery like the Interstate Marine starting battery you have is not intended to be deeply discharged by loads when the engine is not providing charging current. Continually discharging the starting battery with loads when the engine in not running will tend to shorten the battery life. It could also easily leave the battery with insufficient charge to start the engine.

If your boat has an engine which cannot be started by pull-starting techniques, you are completely reliant on the battery for engine starting. In that case it is prudent to have two batteries configured for engine starting, unless you operate your boat only near shore or in water where you could comfortably anchor while awaiting a tow, you ought to give consideration to having two batteries that can be used for engine starting.

Jerry Townsend posted 06-21-2010 09:09 PM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
A main purpose to having dual batteries is to provide a backup power source for starting your engine. Therefore, use two batteries each capable of starting your engine.

The electronic loads we typically have are low - in the range of 0.1 amp - 0.2 amp - and my gosh, with an 80 amp-hour battery, that says that the battery will power those devices (radios in standby, gps, chart plotter, et al.) for a LONG time - and yes, the voltage would eventually drop.

So I don't completely agree with previous comments - as I believe the typical electrical loads we are talking about will not damage a battery - unless a lot of "stuff" is hung on it for a few days. An hour, two or three isn't going to hurt your battery.

Get yourself two batteries, each of which can be used for starting your engine - and a good switch - or a couple of solenoids. Wire it up so that both batteries are charged with the engine running. If you were closer, I would say - bring it over. --- Jerry/Idaho

mrtoyz posted 06-23-2010 01:08 AM ET (US)     Profile for mrtoyz  Send Email to mrtoyz     
Wow, great info guys! I wish I was closer Jerry, I'd really like to take you up on that. I've got all sorts of plans/wants and am trying to plan it all out.

So since I 've got some good info to start could I bug you all for some ideal setup ideas?

I have a 1996 Dauntless 15 with a Merc 75 2cycle. (I believe it produces 10amps)

My list is growing, I'd ideally have/like:
Lowrance Sounder, Finder and GPS combo unit
Portable VHF charging stand
Stereo and 4 speakers
Compass w/illumination
Gauges w/illumination
Later-2 Cannon elec dowriggers and a 24volt trolling motor

Given my plans what would be the ideal battery/charging system? Brand ideas would be helpful...

System I have in mind:

Charging System - Stealth (seems expensive but heard very good things about it. Like the fact I can plug it in in the garage or possible even a solar panel on occassion) Any other similar systems?

Battery switch - unsure if I need one with the Stealth

Batteries - Figure I should get 2 deepcycles (ideally cranking/deepcycle) but unsure of brand or AGM vs Lead acid. Cheapest AGM grp 27 I've found are $116. Cheapest lead acid either Costco grp27($65) or Walmart (~$60). Space is a big issue as this is a small center console boat. Even thought about the small light Optimas at Costco grp27 ($140), problem I see is they have a very low Ahr rating.



jimh posted 06-23-2010 07:52 AM ET (US)     Profile for jimh  Send Email to jimh     
AGM batteries are lead-acid batteries.
David Pendleton posted 06-23-2010 02:46 PM ET (US)     Profile for David Pendleton  Send Email to David Pendleton     
My list is growing, I'd ideally have/like:
Lowrance Sounder, Finder and GPS combo unit
Portable VHF charging stand
Stereo and 4 speakers
Compass w/illumination
Gauges w/illumination
Later-2 Cannon elec dowriggers and a 24volt trolling motor

Which is exactly why I recommended the largest battery you can find/afford, Larry.

I've never known anyone whose net electrical power requirements decreased over time.

David Pendleton posted 06-23-2010 02:47 PM ET (US)     Profile for David Pendleton  Send Email to David Pendleton     
Sorry, I meant Jerry, not Larry.
mrtoyz posted 06-23-2010 04:36 PM ET (US)     Profile for mrtoyz  Send Email to mrtoyz     
AGM=Lead Acid?
If that’s the case then my non AGM labeled Interstate Marine cranking battery is AGM? Or is that both are wet cell?

I understood that there was a fundamental difference between Absorbed glass mat as opposed the stand old lead Acid wet cell. AGM being better.

Please explain.


davej14 posted 06-23-2010 07:59 PM ET (US)     Profile for davej14  Send Email to davej14     
An AGM (absorbed glass mat) battery still uses the same electrolyte as a flooded cell lead acid battery. The difference is that the electrolyte is "absorbed" into a material that is in contact with the lead (think saturated sponge)rather than being liquid in a reservoir.

Because of the design, an AGM cell is sealed and will not spill electrolyte. You must pay attention to the charging voltage applied to an AGM cell because they will vent if the voltage is too high. This is not good because any electrolyte that is lost cannot be replaced in a sealed battery. This gets us to the main advantage of a flooded cell, you can add water to compensate for any electrolyte loss. Flooded cells are also less costly.

If you do a search you will find many differing opinions on which technology is the best. You can do the research and draw your own conclusion.

jimh posted 06-24-2010 07:50 AM ET (US)     Profile for jimh  Send Email to jimh     
An AGM battery requires a well-regulated charging voltage. Many older two-cycle outboard motors have alternators with poor voltage regulation. Using an AGM battery with a charging source that has a voltage output greater than 14.5-volts will result in damage to the AGM battery.

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