How to store SLA batteries for 3 months?

[amberwolf]

Not true. There is a small amount of energy being used anytime the batteries are connected even with a breaker switch. I know this from experience. If he is gone for 3 months it will drain the batteires fully by the time he gets back.

The only way that will happen is if there is something else in the connections that is draining them, such as contamination in or on the cabling that shorts (even high resistance) one battery terminal to the other, or if there is a power meter that is across the batteries even if the switch to the rest of the system is turned off.

The contamination could be anything from salt to dirt to oil, etc., that has mixed with moisture and created something electrolytic that will pass current. It wouldn't have to be much to drain batteries over a few months. I have seen a lot of dirty car batteries that drain quickly when not in use because of road grit that gets tossed up on top of them, never wiped off, and conducting between the terminals (especially if there is corrosion around the terminals themselves, for some reason).

Just having them series connected but with an open connection from a breaker or keyswitch, etc., will not drain them unless something else is completing that connection in some way.


It's also possible the batteries you had happened to be high-self-discharge for some reason, coincidental to being left connected. Not as likely as the contamination shorting the terminals, but possible.

[dumbass]

With a yacht I owned, If left moored and unused for some time the batteries [two] were often unable to turn diesel engine over.
I purchased a small solar panel with a regulator, it had red led when charging and green when charged, switching off solar power.
Every time I went to boat, batteries were fully charged and led green. Also, where the boat was moored, wasn't really sunny weather in winter.
This type of setup should be easy to do at home.

That's not the same thing though because on your boat there are several things that draw current constantly like clocks, alarms and so on. My motor scooter does the same thing. This is why most of us said to be sure all load has been removed from the batteries and there would be no problem leaving them for 3 months.

[D-Man]

Here's what you do: Get a rat and have him sniff the wires. If he takes a bite out of one, then there is current flowing. If he takes a crap on the battery, then no current is flowing and it checks out ok. Make sure you get a genuine test rat.

[Sophisticated as Whatever]

I enjoy all the heated talk. We left the batteries wired but with the switch off. The batteries are clean so this should be a good test of everyone's theories. I'll tell you the results in a couple months. If you haven't seen this before, here's a video of our bike in action:
http://vimeo.com/14977250
Thanks guys.

[dumbass]

I enjoy all the heated talk. We left the batteries wired but with the switch off. The batteries are clean so this should be a good test of everyone's theories. I'll tell you the results in a couple months. If you haven't seen this before, here's a video of our bike in action:
http://vimeo.com/14977250
Thanks guys.

Heated talk????

You say you turned off the switch but are you sure the switch is the main cutoff for the battery power and nothing else is connected before the switch?

Bob

[Solcar]

I'm not sure how the intrinsic voltages of those SLAs compare to the flooded lead acid in my car, but my experience is that a fully charged car battery will settle down to 12.8v after several hours of time during which the surface charge wears off. That seems to be the same as what I've read or heard, too.

Since I am compulsively averse to cars anymore and only drive in a real pinch, the car can sit for a year at a time before I find an excuse to run it. What I've decided to do for the battery is to build a charger using a wall wart and a LM78L12 with an added forward biased 1N4148 diode in series with a 100 ohm resister between its regulation pin and ground. That makes it put out 12.8v, which I am keeping connected to the battery all the time.

I have heard that the maximum longevity of a car battery in storage occurs at about 70% of full charge. That makes sense to me considering that more charge will increase the chemical activity inside the battery, that is, self-discharging; and discharging and charging consumes the plates eventually. After all, a completely dead battery will eventually reach a state of total inertness given enough time in a closed system.

I'm figuring that 12.8v is a good minimal point that provides a little margin above the 12.6v that i recall as the 70% charge figure. I'm going for a compromise between the two voltages since holding the terminals at 12.8v might not be the same situation as a battery that is holding at that voltage on its own.

i have read that it is good to float a car battery between 12.8 and 13.5 volts. The literature meant steady state, not going up and down, though. However, even cycling between 12.8v and 13.5v is probably the same effect-wise as holding it say, 13.15v.

After all is said and done, the usefulness of these ideas depends at least partly on the differences between car batteries and rechargeable SLA batteries. Either way, I thought the they might help someone.

[amberwolf]

I wonder how it turned out for the OP?

[Solcar]

I hope it went well. I hadn't realized when I described my trickle charging project above that they were from the same area as where I live.

In the meantime, I had started my car once early last fall and decided that the battery was not strong enough and that my trickle charger was a bit too conservative in it's attempt to maximize the battery's life. So, I changed the voltage regulator circuit a little to put out about a tenth of a volt more, to a little over 12.9v, if memory serves me. Hopefully, I'll soon see how that has turned out after it has been on the battery for over six months.

[The fingers]

Save-A-Battery charger can be left hooked up for extended periods. It brought my batteries back to like new performance after being attached for several days as they started to sag when 6 months old. They come in a variety of voltages and may double the expected SLA battery life.