All About Boat Batteries

[ris]

We have been using the Balmar gauge for about 4 years on the same set of batteries. We move the gauge and the batteries from the boat to our travel trailer. We use four Trojan 105 batteries on the boat and trailer. (6 volt deep cycle batteries) That is our only bank of batteries for the boat. One boat one bank of batteries. They start the boat and are the house batteries. If for some reason the batteries all just died overnight we carry one of those Tacklife car jumpstarts. We have used it on several trucks with dead batteries and a diesel bobcat. It is supposed to be able to jump a car up to 40 times. All I need is once on the boat in order to get to a marina or back to the boat ramp. Does anyone else just use one bank of batteries or do most folks use a separate battery for the motor.

Richard

[Jimmyt]

We have been using the Balmar gauge for about 4 years on the same set of batteries. We move the gauge and the batteries from the boat to our travel trailer. We use four Trojan 105 batteries on the boat and trailer. (6 volt deep cycle batteries) That is our only bank of batteries for the boat. One boat one bank of batteries. They start the boat and are the house batteries. If for some reason the batteries all just died overnight we carry one of those Tacklife car jumpstarts. We have used it on several trucks with dead batteries and a diesel bobcat. It is supposed to be able to jump a car up to 40 times. All I need is once on the boat in order to get to a marina or back to the boat ramp. Does anyone else just use one bank of batteries or do most folks use a separate battery for the motor.

Richard

I use one house battery and one cranking battery. I don't carry a jump box.

[Jimmyt]

Looks like it took a charge. Can't wait for the load test. Great documentation!

The Beckman 310 has good specs. If it's still in good shape, it should be fine for what you're doing. In fact, the free HF meter is reading right there with it, so it may be good enough too. I'd check it at a couple of other voltages against the Beckman just to be sure.

After all, you're not doing certification testing.

[Inquisitor]

We have been using the Balmar gauge for about 4 years on the same set of batteries. We move the gauge and the batteries from the boat to our travel trailer. We use four Trojan 105 batteries on the boat and trailer. (6 volt deep cycle batteries) That is our only bank of batteries for the boat. One boat one bank of batteries. They start the boat and are the house batteries. If for some reason the batteries all just died overnight we carry one of those Tacklife car jumpstarts. We have used it on several trucks with dead batteries and a diesel bobcat. It is supposed to be able to jump a car up to 40 times. All I need is once on the boat in order to get to a marina or back to the boat ramp. Does anyone else just use one bank of batteries or do most folks use a separate battery for the motor.

Richard

I think its a matter of 's can hold two under the steps so we do. If I recall (never been inside) 's only have room for one battery????

[Inquisitor]

Looks like it took a charge. Can't wait for the load test. Great documentation!

The Beckman 310 has good specs. If it's still in good shape, it should be fine for what you're doing. In fact, the free HF meter is reading right there with it, so it may be good enough too. I'd check it at a couple of other voltages against the Beckman just to be sure.

After all, you're not doing certification testing.

Oh! It's in good shape... from original Styrofoam box, in plastic bag, power cord with twisty and with manual and warranty card... You'd be hard pressed to tell it didn't just come off the shelf. My Granny was the same way. Once showed me an old Kodak Brownie camera... same thing with box contents AND she was even more excessive... had the store bag with store receipt. Guess its a Depression Era thing.

That mold got broken some where along the way Dad didn't share his equipment with me. He'd rather buy me my own tools than let me borrow his.

I brought Batty over to Dad's, but not all the discharge gear. But, she's getting a good rest... which brings up another thing:

16 hours of resting
H.F. 12.92 V (Same as last night)
Beckman 12.84 V

She's not settling on 12.7V. What's up with that?

[Jimmyt]

Any number of things that you probably shouldn't worry about; slight over charge, variations in manufacturing, meter error, etc. The important part is, you've let it rest and it's fully charged, possibly a tad over 100%.

I have had the misfortune of losing several folks from that era. They were something special. They epitomized the phrase "do more with less". We could use more of them these days. I'd love to see what they could do with the tools and tricks we have available now! I've "inherited" many items that were still in original packaging. There were even a few items that had never been opened.

[Inquisitor]

Back, testing with the battery on my desk. Let it rest for 54 hours and it settled on a setting of 12.92V.
Another aspect learned that JimmyT clued me into... It took about 3 hours, 40 minute after removing from charger for it to "Rest" to this 12.92V.
Here is the graph for those interested in kind of detail (like me)



I've started the capacity discharge test.

[Jimmyt]

Very interesting. Was the battery subjected to a temperature change around 24 hours in? Trying to rationalize the slight hump in the middle.

[Inquisitor]

Very interesting. Was the battery subjected to a temperature change around 24 hours in? Trying to rationalize the slight hump in the middle.

I wish I could explain the hump. But no... that was still at Dad's house with a very constant 70F with no movement. I can't explain it from environment. The time between the last two data points was when it was moved to the car, made the trip (~ freezing ambient) and letting it warm up over night back on my desk.

[Jimmyt]

Near a window? Any solar influence? Unless the thermostat was near the battery, the temperature may have varied somewhat.

Interesting. Especially so if there is no explanation.

[Inquisitor]

... Any solar influence? ...

Yeah! It received 42 gamma particles from the sun in that time period more than the previous hour.

It was directly under a ceiling fan that is always on. I suspect the temperature was more constant than the Harbor Freight volt meter.

[Jimmyt]

Yeah! It received 42 gamma particles from the sun in that time period more than the previous hour.

I was thinking a little longer wavelength, but good to know.

[Inquisitor]

Here are the results of test for the 8/2013 Autocraft Deep Cycle Marine / RV battery. Typically the amp-hour rating shown for batteries is a test where it is discharged at a rate of C/20. In theory this battery started life as an 80 amp-hr battery. I would have liked to find a constant 4 amp load, but I ended up using the boat fridge that draws 3.3 amps when on MAX. I am actually using the energy to do a test on the fridge as well. Because of this, the amp-hour rating I found is somewhat higher than what would be found if actually discharged at C/20 = 4 amps.

For the sharp eyed - JimmyT.
At 9:40, the yellow highlight puts a knee in the data. This is where the thermostat on the fridge was satisfied, compressor stopped and the current went to 0.09 amps. I'd like to say I pre-planned this but blind-dumb-luck did give me a chance to see what the rebound voltage would be after a short rest. As indicated, I show a rebound voltage of 0.22 volts. This was used later in the test to determine the voltage to stop the test = 12.20 - 0.22 = 11.98 volts. Sure enough after stopping the test at 11.98 volts, the voltage rebounded to 12.20 volts after about ten minutes.



Summary
It is my current belief that an advertised amp-hour rating is for a 100% discharged battery. JimmyT speculated that amp-hour rating might be for the 50% safe level. If anyone knows for sure, let us know. I have not been able to find anything indicating either is correct. The only other data I could find was saying that the 50% state of charge (SOC) was for a rest voltage of 12.20 volts. I also found that when discharged to 100% the life of even a deep cycle battery is around 130 - 250 cycles.

The battery does not show any really bad behavior. For instance it does not load up and suddenly die. It follows the normal discharge curve shape. Unfortunately, if the ratings represent a 100% discharge, then I now have a 44 amp-hour "rated" battery. If JimmyT is correct, I only have a 22 amp-hour battery. Either way, I really only have 22 amp-hours I can count on.

[chipveres]

Ouch that hurts. 22 amp-hours from an 80 amp-hour rated battery? And your test technique seems very realistic. I know from long experience that when a battery-powered radio quits the first thing you do is change the battery. This is one case where I hate to be proven right. You paid for all 80 of those amp-hours.

Chip V.
s/v Sand Dollar

[Inquisitor]

Ouch that hurts. 22 amp-hours from an 80 amp-hour rated battery? And your test technique seems very realistic. I know from long experience that when a battery-powered radio quits the first thing you do is change the battery. This is one case where I hate to be proven right. You paid for all 80 of those amp-hours.

Chip V.
s/v Sand Dollar

That is at SOC of 50%. Its like someone with a brand new 100 ah battery, they really only have 50 ah to use. (why I'm going Lithium on the house side). So my 44 ah rating... says I've lost about half its capacity... and its seven years old. That a pretty good life, from what people are saying.

Now, that its being shifted over to used as a starter battery role, I know it has the depth... I just don't know if it has the oomph. I noted earlier, the Merc 60 seems not to turn over with quite the verve it used to, but it seemed I could crank it all day at that lower rate. This test confirms that. It just the max cranking amps is marginal for starting. New it says, it has 550 cold cranking amps. If that is cut in half also, then I only have 275 cold cranking amps.

Anyone know how to go about testing CCA?