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Old 13-12-2011, 16:27   #1
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Load testing my start battery

Well it finally happened. After 2 months of neglect I tuned the key on my trusty John Deere and ... almost nothing.

After a little more prompting she finally wheezed into life, hunted a bit and then settled down to her usual roar. A trip up and down the harbour, bit of rolling on a mooring by the Zoo, press the start button again and the new girl is back to her usual self.

Now I'm thinking start battery. It must be around five years old by now, so it's not going to be in its prime. But buying a new one is going to be expensive, they're heavy, and I have to dismantle a fair bit of cabinetwork to get it out, not to mention the "upgrades" I really should do at the same time.

A bit of hunting on the internet brings up battery load testers, but there's a myriad of them available for widely differing prices. Some even available off Ebay in Oz.

It's a confusing array of features, prices and brands. Some do 6V and 12V (nice to test the house batteries), others will test start motor, alternator and probably clean out the wires as well.

So does anyone have any experience of them? Do they work, what features do I need, are the el cheapos any good or should I plunk down for a good "name" brand?

Or should I go back to the good old days of density testing, voltmeters, thermometers and data charts? Can I really build my own out of a few bits of string and some burnt toast?
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Old 13-12-2011, 16:42   #2
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Re: Load testing my start battery

Here's what I was using during and after working in the alt and starter rebuild business. The little button puts a load on the battery (carbon piles) and if the battery holds up for a minute or longer, she's good for a good while. One of my many boat tools. It can also test the alt output.

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Old 13-12-2011, 17:35   #3
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Re: Load testing my start battery

I agree, rent or borrow a battery tester that puts a relatively short term, big load on the battery.
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Old 13-12-2011, 18:55   #4
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Re: Load testing my start battery

Gosh it's nice to see someone else keeps GOOD Old tools besides me LOL I just found a pretty good one in a garage sale down the Bayou, so now have a spare, if you have more the a couple of batterys you should have one of these, they are still available new ck you nearest auto part imporium ! Bob and Connie
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Old 13-12-2011, 19:28   #5
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Re: Load testing my start battery

Thanks to all so far.

Am I to assume that almost all testers that put a load on the battery will give some sort of useable result?
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Old 13-12-2011, 19:43   #6
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A new battery may be the ticket but...

If the boat was unused for 2 months did you have any charge source floating the battery?

A 5w solar float charger connected to the start battery may be all you need. There are a few reasons the battery will discharage on its own over time.
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Old 13-12-2011, 20:19   #7
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Re: Load testing my start battery

Quote:
Originally Posted by Boracay View Post
Thanks to all so far.

Am I to assume that almost all testers that put a load on the battery will give some sort of useable result?
Yeah! There's cheap ones and good ones. Some have a twist dial on the carbon pile and some have buttons. Some are rated for standard car size batteries and others bus size batteries. The specs should be on a label on the instrument. The good ones will be CCA 500 amps or higher.

Or you can just take them to a battery vendor and they'll most likely test them for free, hoping on a sale (do watch the test).

One more note; If you open up the caps while testing and one or more cells boil violently then it's a bad cell(s). If they boil slightly and equally after several seconds then probably OK. Depends on the carbon load.
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Old 13-12-2011, 20:31   #8
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Re: Load testing my start battery

I do have a 10W solar panel charging the battery through a basic controller, but I've also run the bilge pump off the battery, so it could have gotten a bit much.
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Old 13-12-2011, 20:36   #9
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Quote:
Originally Posted by Boracay
I do have a 10W solar panel charging the battery through a basic controller, but I've also run the bilge pump off the battery, so it could have gotten a bit much.
Yup... Time for some maintenance - LOL...
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Old 16-12-2011, 13:48   #10
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Re: Load testing my start battery

The story so far:-

I rang my not so local but friendly battery supplier and determined that my battery is a N120. Replacement cost about $250 (trade in and discounts applied), but I have to get the 41kg battery from the boat, to him, and the new one back on the boat.

After some thought about the load tester I realized that I had a load ready to apply (the starter motor). Conversation with the above supplier suggested that if the battery was above 10V when the stater was used then it should be OK.

I also had a chat with the marina mechanic. He suggested that the battery needed replacing and he could source one for about the same price and help me to put it in.

I put the digital voltmeter on the battery and had "crew" start the engine. Of course it started quicker than the twinkling of an eye but battery voltage only looked to drop to 11V. Probably not relevant is that the battery cold read 13.67V, charging it topped out at 14.15V.

My feeling is that the battery is on the way out, that it does not hold charge the way it used to. Christmas not being the best time to get anything done in Oz I'll get the mechanic to order a new battery and put it in as time permits.

I've also changed the fuel filters (at 80 hours) just in case.
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Old 16-12-2011, 14:54   #11
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Re: Load testing my start battery

Borcay,
For quite some years I sourced the batteries for my car from the local scrapyard at $1.00 a time.
People often seem to throw away batteries that have some life left in them.
Your boat should have alternative starting battery, so it should not matter too much if the dedicated battery starts to fail.
Why not use it until it is really bad?
On another note, the best thing I did for our boat's batteries, was to add some solar panels to give them a float charge when unused.
Regards,
Richard.
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