Determining AH rating of aging batteries

BFL13 wrote:
Run the ten hour test at the 20AH rate to see how long it takes to get to 50% (50% measured by SG and confirmed by voltage after waiting an hour after removing the load)

240AH 20 hr rate is 12 amps ( four 3 amp lamps or whatever) Use the Trimetric AH counter for more confirmation.

Say it takes 9 hrs to get down to Trojan's 50% SG of 1.172 and after an hour of bounce back you are nearing 12.1v so you are at about 50%

9 out of 10 is 90% or 216AH of 240 (Trimetric AH count for comparison cross-check)

If you use lamps then they dim as voltage drops and your 12 amps gets less so turn on more lamps as test goes on. If you use an inverter and some load to get 12a then you get inverter creep up in amps as voltage drops so in that case start with 11 and end with 13 to get 12 average.

If you are lower in capacity then try a serious session of overcharging at 15.5v to see if you can get the SG up if some of the sulfation is not yet permanent.

Without reading this post first, I ran a 12 amp load for 10 hours, the voltage was down to 11.9 on my trimetric, but after reading your post I shoulda let them 'come up' for an hour after my test?
Guess I gotta run it again..?

CHEATERS!

Now your local battery guy can't afford that new BMW. Some friends you are :)

Ya, I need to do it more often.

Past years I took the batteries out over the winter and charged them once a month, this past winter I left them on the trailer and plugged the trailer in once a month for a day, wonder what's best over the winter?

Well, a couple of years back, I had the same problem with my 3year old Interstate sixers, seemed like no matter how long I ran the genny I could not get them to rise much above 85% SOC (per LinkLite metering)...They had never been EQ'd. So after scanning the forum (thanks Guys!!), and trying out the EQ drill they immediately responded to back to normal again...I've been doing the regular EQ's (approx. every 5-6 wks) ever since...Batts now 5 1/2 years old and still going strong...

3 tons

OK, haven't run the test yet but I checked the SG of the cells before I started equalizing, 1 cell was really low, 1100 or something.
Started the equalize mode on the B&D, took 5 hours for it to do it's thing and now all cells are above 1275 so I'm thinkin that was the problem on our last trip

Guess I don't maintain my batteries as well as I should, tomorrow I'm equalizing my fishing boat batteries too.

Screw all the other tests.

Fully charge at 15.0V at around 77F.

Equalize charge at 16.0 V until the Specific Gravity on all cells gets to 1.280, or the voltage at the battery terminals reaches 16.0V, then shut the manual charger off. Your manual charger is capable of a full 16.0V, isn't it? If not, get something around 10-15 amps that is capable of a full 16.0V

Log the SG of every cell on every battery.

Don't assume on the voltage being recharged with, measure it with a digital multi meter.

Don't assume on the specific Gravity, measure it with a Freas #1 hydrometer, with temperature correction.


Report the results here.

Then do what you need to do to recalibrate your trimetric.

On another note, it is possible that if you seldom use the RV that over a period of time, getting a false % SOC reading on your metering...This 'may' happen after a prolonged period of inactivity (RV non-use) where a small amount parasitical losses (say, rv circuit boards) overtime occur...Over a period of time, these slight losses can produce an unwanted (stray) accumulation of magnetic flux lines across the metering shunt (inserted into batt Neg Cable) thus a resulting phantom SOC% reading. The remedy for Xantrex LinkLite metering (not sure about Trimetric...) is to do a manual synchronization (basically a reset - a return to 100% SOC) after confirming battery is fully charged.

3 tons

Fisherguy wrote:
Thanks Barry, will try that this weekend.
Yes they have 3ton, use my B&D charger and will do that again before doing the test.
Do you guys disconnect one side of the battery before equalizing? Shouldn't have to, right? (I'll turn off PD)

Yes, be sure to disconnect one side of batt before EQ so not to harm RV electronics...

Thanks Barry, will try that this weekend.
Yes they have 3ton, use my B&D charger and will do that again before doing the test.
Do you guys disconnect one side of the battery before equalizing? Shouldn't have to, right? (I'll turn off PD)

12.1v after a full charge?? Try verifying with a voltmeter at the batts. Check output volts at the converter/charger, if all is good then go with equalization...BTW, now 5 years in, have these batts ever been equalized??