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outback
10-27-2014, 12:14 PM
Between our motorhome, boat, and other vehicles, I own a number of wet cell batteries. The motorhome alone has 4 deep cycle batteries and a chassis battery for cranking.

NAPA has a load type battery tester, made in China, for $57.

Got to thinking I have a 12VDC motor from a tread mill. Could I use that as a load then measure the battery voltage?
How much load do I need to test a battery? What drop in voltage determines if the battery is shot?

I also have some ceramic resisters in my basement bone yard. Maybe I could use those for a load.

Should I just buy a tester and be done with it?
Thanks,
Jim

CarlByrns
10-27-2014, 12:20 PM
Buy a tester and be done with it.

The load test info is available from the battery manufacturer and may even be on the battery itself. The load tester will have instructions on how to use the CCA rating to determine the test current (usually they're the same thing, but not always).

MichaelP
10-27-2014, 12:52 PM
Harbor Freight sells a 6V/12V 100W battery load tester for $21.99. It works just fine.

Paul Alciatore
10-27-2014, 01:37 PM
Selecting a load for testing an automotive type battery is not completely simple. A starter can draw hundreds of Amps. and different vehicles can be a lot different. I once saw a V8 starter slam a 500 Amp test meter HARD against the high end. And, no, the starter and engine and battery were all perfectly OK. A starter ON AN ENGINE is the ultimate test load.

I have a small device that plugs into the cigarette lighter socket. You insert it and crank the engine. The red LED lights if the battery Voltage drops below a preset level to indicate a bad battery. I have another device called the Battery Marvel. It is microprocessor based and wired directly to the battery, under the hood. If the battery Voltage drops too low, it sounds an alarm. I do not know if it would work on smaller systems, like motorcycles or snowmobiles. It is definitely 12 Volts only. I think devices like these are a better way of judging automotive battery condition because most other testers use a far lighter load.

http://www.batterymarvel.com/

All the usual disclaimers.

outback
10-27-2014, 01:56 PM
We just bought this motorhome 2 weeks ago with a 30 day warranty.
Did a test run last week and 4 deep cycle batteries failed to run the furnace past 3:00 AM. Managed to get the generator started off
the chassis battery so we could run the furnace off the generator power.

The Winnebago dealer said if the batteries are shot they will replace them under the warranty. Problem is it will cost $50 in gas to get
the motorhome back to the dealer. I need to be fairly certain the batteries are shot.

I think I'll go ahead and buy a tester so I know for sure the batteries are shot or not. I just finished topping of the batteries with distilled water. Three quarts of water to fill 4 batteries. Also cleaned all the battery terminals and coated the connections with a
dielectric grease (Noalox). Batteries have a very short life expectancy when the cells go dry. We shall see.
Thanks,
Jim

Jon Heron
10-27-2014, 02:22 PM
Deep cycle batteries also have a short life expectancy if left sitting without a charge for any length of time... Or at least so I am told by my battery shop.
Cheers,

flylo
10-27-2014, 02:38 PM
Deep cycle batteries also have a short life expectancy if left sitting without a charge for any length of time... Or at least so I am told by my battery shop.
Cheers,

But if taken care off they last a long time. I had 6 golf car 6V that were over 12 years old still doing great running the cabin thru an inverter until my son left the system on & I didn't discover it till 3 months later.

MaxHeadRoom
10-27-2014, 03:31 PM
The (fairly Cheap) tester I picked up gives a 150amp load test and the rate of discharge displaying the health of the battery is recorded.
You should not use a starter motor off the vehicle, one, it does not load the battery, two, being a series motor it operates in a runaway condition and the rpm is governed purely by any load or windage.
Max.

CarlByrns
10-27-2014, 05:01 PM
Selecting a load for testing an automotive type battery is not completely simple.

But if you use a standardized test, it is repeatable and you can build a knowledge base off the data.

For years the standard tester in a professional garage was the Sun VAT-40 analyzer that measures battery voltage and amperage simultaneously which is the only correct way. All professional load testers still work just like the VAT-40 only automated and with digital readouts.

Lead acid batteries will build a 'surface charge' that will show a dead battery as 'good' to lighter-plug doodads. The battery will have a voltage reading of 12 to 14 volts but will not be capable of producing more that a couple of amps. Hence the need to pull a load to get an accurate voltage reading.

CCWKen
10-27-2014, 08:10 PM
And, you can't load test a dead battery. It has to be fully charged to test. If you can't fully charge the battery, it's shot. Get a hydrometer and a load tester and perhaps a good battery charger. Don't peck around with a bunch of crap out of the scrap bin. A new battery is way more than $50 and if you have a lot to maintain, the tools will pay for themselves after the first year.

JMHO

J Tiers
10-27-2014, 11:52 PM
All the deep cycle (real ones) batteries of the type you likely have that I know about are 6V. Any 12V may be some sort of "marine deep cycle", aka trolling motor batteries, NOT the same thing in any way. Or maybe they are starting batteries, relabeled.

Anyhow, CCWken has it. If it isn't worth $50 to get them to the dealer, you can use whatcha got. A good Trojan Mileagemaster T105 costs around $140 less core. Those are 6V and can last 10years if treated decently.

CarlByrns
10-28-2014, 12:14 PM
All the deep cycle (real ones) batteries of the type you likely have that I know about are 6V. Any 12V may be some sort of "marine deep cycle", aka trolling motor batteries, NOT the same thing in any way. Or maybe they are starting batteries, relabeled.


Mmmm, not quite true. While the vast majority of 12 volt deep cycle 'marine' batteries are indeed relabeled car batteries, there are true 12 volt deep cycle batteries out there. I had a pair for my camper that worked great. Bought them at an industrial battery supplier, not a parts store or marina.

The easiest way to tell if a battery is a true deep cycle is to look at how it's rated: if the label has a cold cranking spec, it ain't a deep cycle.

Willy
10-28-2014, 12:55 PM
I believe a lot of confusion about 12v vs 6v deep cycle stems from the 6 volt battery's ability to maintain higher sustained discharge rates.
Nothing wrong with a quality 12v deep cycle battery, it's just that they don't have the inherent amp hour rating of a 6 volt.
Mind you many applications require 12 volts to operate, so now one is torn between one 12v or 2 6v batteries in series. The cost for the 2 6v batteries is going to much higher, but look at the specs of the 2 deep cycle batteries below, one 12v, one 6v.

12 volt deep cycle battery

(http://usbattery.com/products/12-volt-batteries/us-12v-xc2/)
6 volt deep cycle battery

(http://usbattery.com/products/6-volt-batteries/us-250hc-xc2/)There is absolutely no comparison in the amount of work one can obtain from two 6v batteries wired in series vs one 12v. This in spite of the 12v workload requiring less amperage. Probably the main reason one sees most golf carts and industrial users turning to 6v batteries.

darryl
10-28-2014, 07:53 PM
Given that the size of the battery roughly determines how much active area there is to produce current, a battery of 2 6v ones would be roughly twice the size of a single 12 v one. In terms of output power, if you combined smaller 6 volt deep cycle batteries into one 12 volt package of roughly an equivalent size to a typical 12 volt one, you would get about as much power from that. Of course, the 6 volt deep cycle batteries (all that I've seen anyway) are 'full size', so it's pretty safe to say there's more output capacity when they are combined to make a 12 volt output. The basic premise here is that the larger the individual cell, the more capacity it could be capable of, both in peak current and amp/hour.

Beyond this, of course there are other differences- some have heavier plates and would be physically larger for the same capacity, and some have deeper containers which do nothing for capacity but do provide for a longer lifetime in general.

I find that in the general consumer market, you have to be aware that what is called 'deep cycle' generally isn't. If you are in need of a true deep cycle battery, then you have to find exactly that. As mentioned, the T105 does qualify in that regard.

Ironwoodsmith
10-28-2014, 09:33 PM
If your battery bank won't run the furnace through the night and it consists of 4 charged batteries than it is not a good one. I have done many rv and marine systems and know the basics of a good system. A true deep cycle battery will have very heavy plates and a lot of lead in them. They are rated at a 20 hour rate. So if they are 200 amp/hour for example, than they are rated to put out 10 amps steady for 20 hours. Because of the heavy plates they don't have as much CCA's as starting batteries do.

You will not get great batteries from the average rv lot. They will try to put some off-brand or at best an Interstate marine battery in there. If you can get them to give you the cash instead you can get some real quality units from an internet company. I used these guys in Grants Pass, Oregon. Prices are good and shipping on multiple units is near free.

http://www.batterystuff.com/

I am replacing the batteries in my own coach right now as well. My coach uses 8d batteries. Four of them. I am going with AGM batteries. Sealed but still a wet cell battery, not in the conventional sense, but they charge and act like wet cells. They are not gel cell batteries.

If you want your bank to last for 5 years or more than size it to run down only 25% to 30% between charge cycles. Anymore and you will damage the plates over time. Look into a pulsing unit. It is like a capacitor that use the battery's own power to deliver a high voltage pulse continuously. Many experts agree that it vastly improves the longevity of a battery. I am installing two of them on my bank. They are $40 a piece.

What size are your batteries, the class? Golf cart batteries do not fit where most batteries do. They are taller with a smaller foot print. What do you have for a charger? The older style convertors in MH's do not do a good job of charging a battery bank. They actually do a pretty good job of killing them slowly. Do some reading on charge cycles.

Paul Alciatore
10-29-2014, 12:42 AM
...<snip>...

Lead acid batteries will build a 'surface charge' that will show a dead battery as 'good' to lighter-plug doodads. The battery will have a voltage reading of 12 to 14 volts but will not be capable of producing more that a couple of amps. Hence the need to pull a load to get an accurate voltage reading.

YES! And that is precisely why the instructions for my "lighter-plug doodad" say that it should be read WHILE CRANKING THE MOTOR WITH THE STARTER. That is the largest load that an automotive battery will ever see and that is what it needs to be capable of delivering. So that is the best time to test it. Or at least as good as using a standard load. It has a green LED that indicates 12 V and a red LED that only lights when the Voltage drops BELOW a set point, some where around 7 V (I forget the exact value). The green one should come on and the red one should not when you use the starter. In the past it has been quite accurate in showing when a battery (or the charging system) is going bad.

The hard part is determining weather it is the battery or the charging system that is at fault. I am going through that now with my wife's Volvo.

Ridgerunner
10-29-2014, 06:35 AM
How do those RV's charge the different type of batteries? Doesn't the deep cycle batteries take a different charge rate than that of a start battery?