How much my batteries discharged over 6 months

[idroba]

I just thought I would post some information on the batteries in my Argosy 20. They were new last summer, and are a pair of 6 volt golf cart batteries in series, purchased from Costco.

The converter/charger is a 3 stage Progressive Dynamics 9245. The batteries were left in place (as I always do) but totally disconnected with a Perko marine switch so there was absolutely no draw on them. I go to Arizona for 5 months in the winter, and so it has been about 6 months since any charge was put on them. Winter temps here run in the teens to 30's most of the time.

I have a very accurate shunt fed ammeter on my batteries, so I can see exactly how much charge is going in or out of them.

I connected them via the Perko switch, turned on the PD converter/charger and read 2 amps on the meter. Within 15 minutes that had dropped to 0.5 amps. So, they did not discharge to any significant extent over the 6 months of sitting unused and disconnected.

I just thought the information might be of interest to some of you.

[TouringDan]

Thanks for the information. What kind of meter do you use for measuring current?

Dan

[idroba]

Originally Posted by TouringDan

Thanks for the information. What kind of meter do you use for measuring current?

Dan

I have a post on it titled "Ammeter and shunt system" under electrical>batteries and converters. I know there must be a way for me to give you a direct link to that post, but I haven't figured out how. So, do a search of that topic and you will find it, along with photos.

[Bruce B]

Did you note the batteries voltage before you connected the charge source? I am just wondering because I have run into sulfated batteries that will not take a charge (charge amps drop quickly, voltage comes up fine but they have no capacity!). One of the things I like to see is good voltage before I apply a charge. Then of course I like to actually measure capacity every few years to see just how well I am doing.... the best results have always been with my agm's. The results can be quite enlightening!
Bruce

[idroba]

Bruce: I agree with you on sulfated batteries which will come up to voltage quickly, but have no capacity. I did not take a voltage reading prior to putting them back into service. The batteries are less than a year old, and I know they are good, and have not sulfated. I have used this technique of total disconnection and leave in place for many years. The Trojan's that I took out last summer had 10 years on them and were finally beginning to show signs of reduced capacity due to age.

I find the main thing that kills batteries when sitting is the slow drain caused by tiny phantom loads. They slowly, over months, become discharged and sulfated, and in the spring will never come back up to capacity. That is why I have gone to Perko switches in my rigs. When they are shut off, nothing can discharge the batteries, assuming the tops are clean and dry.

The hardest phantom load to locate I ever had was the power operated motor driven Skyliner antenna on my AS 310 motorhome. This was not the antenna amplifier, but the motor drive itself. Even when off, the electronics took power, about 15 mA as I recall, which over months, killed batteries. I finally found it, and put a real on and off switch on the line to the power antenna motor.

[bryanl]

re: "I have run into sulfated batteries that will not take a charge" -- generally, the older the batteries, the more the sulfation, the higher the impedance, and the higher the self discharge rate. That means they act like smaller batteries capacity wise.

For new batteries, the self discharge rate is usually rather low, like a couple of percent per month (compared to a couple of percent per week for old batteries).

To me, it is sad to see that a system (PD9245) with a very decent battery maintenance mode is being unused. A battery sitting is a battery growing lead sulfate crystals. Longer times means the crystallization gets hardened and that is very difficult to reverse.

re: "So, they did not discharge to any significant extent over the 6 months of sitting unused and disconnected." -- discharge isn't what will kill the batteries. What does them in is sitting around without a top charge and doing nothing to inhibit sulfation buildup. That's what the PD 9245 will do if you give it the chance.