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Old 09-04-2012, 18:29   #1
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7 AH AGM for running Nav and sounder

I just bought a tender for the big boat



and will want Bilge pump, nav lights and a small sounder on board and was wondering how these 7ah AGM batteries for $22 would go.

Would they have enough grunt to run for several hours if needed?

7AH 7 AMP HOUR BATTERY AGM SLA UPS ALARM RECHARGABLE 12 VOLT 12V + BONUS | eBay

Main site for manufacturer here Sealed Lead Acid | Powersport | NiCd and NiMH | SLA Chargers | Power-Sonic Batteries
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Old 09-04-2012, 20:13   #2
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Re: 7 AH AGM for running Nav and sounder

I would go bigger. My motorcycle has a 12aH AGM and is almost dead after running the stereo for a couple hours.
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Old 09-04-2012, 20:14   #3
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Re: 7 AH AGM for running Nav and sounder

7Ah isn't much but most of your loads are small. Presumably you'll charge it from the outboard. Your big draw item is the bilge pump. Find out how much current it draws & divide that number by 7 to see how long the battery will power it. If the bilge pump draws 2A, the battery will power it for ~3.5 hours (probably a bit less, as that 7Ah rating is for a 20 hour rate).

One issue is that AGM batteries require a different charging regimen from a standard wet-cell. If you over charge them, they'll die very quickly. You should check what voltage the OB charges at. Most OBs I know are unregulated, which probably isn't what you want.
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Old 09-04-2012, 21:30   #4
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Re: 7 AH AGM for running Nav and sounder

Thanks Jon, its no problem, I do have a spare car battery doing nothing so it looks like that will be the one to use.
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Old 09-04-2012, 22:25   #5
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Re: 7 AH AGM for running Nav and sounder

I would definitely go slightly bigger. Either that or pick up two. They do not appear to very space/weight consuming. Caveat... I am mildly paranoid about running out of power.
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Old 09-04-2012, 23:20   #6
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Re: 7 AH AGM for running Nav and sounder

Alarm batteries don't like being deep cycled. How long it would run things depends on how much power they run but I'd guess $50 would buy you a lot more deep cycle battery at Walmart or Sams club.
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Old 10-04-2012, 00:05   #7
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Re: 7 AH AGM for running Nav and sounder

Quote:
Originally Posted by hellosailor View Post
$50 would buy you a lot more deep cycle battery
$50 wont buy a second hand no name piece of crap in Australia.

Quote:
at Walmart or Sams club.
None of which exist in Australia

The car battery I had ends up being a marine battery and a fairly large sucker at that.
Bigger than the single battery I had in my 10m ft cat running a heap of gear and an electric start motor.

Probably a bit of overkill me thinks.
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Old 10-04-2012, 12:19   #8
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Re: 7 AH AGM for running Nav and sounder

Oh, OZ. Sorry to hear about that, my condolences. <VBG>

Surely, you've got some kind of equivalent? Some big-box buying club or company known for selling things relabelled as their own?

The $22 for a 7AH AGM is quite comparable to the price in USD for the same thing here. Batteries of all kinds here often have a 2:1 difference in price for the exact same battery from different vendors. Unless you've got, what? Stiff tariffs or excise taxes on car batteries?

Another niche is to try contacting a local amateur radio club. There's often someone in the local utility company who gives them two-year-old deep cycle batteries FOR FREE, or dirt cheap, because the backup power batteries have to be changed every second year even if they've not been used. That's not new, but often is in very good condition.
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