Deep Cycle Lead Acid Batteries

Hi all-

Hopefully I'm posting this in the correction section.

I have a 3 year old deep cycle, lead acid battery that I brough home and filled with acid about 3 years ago. It's used as a power supply to my battery sump pump, which is the back-up in case the main electric pump fails.

The battery has been connected to what I assume is a trickle charger for the past 3 years (basement watchdog-type device). It is never competely discharged, and the most "load" it sees is a monthly 30 second test of the battery powered sump pump. I haven't performed any maintenance on the battery except keeping it clean of dust. I haven't had to add any water to the battery.

My question is how long a life does a battery like this have under the above mentioned conditions? Do lead acid batteries tend to lose their effectiveness over time? I've read that the battery needs to be replaced every 4 years or so, but that's from the manufaturer and they of course want to sell batteries. Is that a realistic assumption for battery replacement, or do they tend to last longer if kept filled with fluid and charged?

Thanks,
ualdriver

 

Batteries in this condition will last quite a long time if properly cared for. Even if "slightly" abused as yours has been. Some of the batteries in my bank are going on 7 years and still going strong.

If you have a charger capable of it, I would give the thing an equalize charge and desulphate session. The equalize charge is especially important in this case because it has been sitting there with absolutely zero motion for years. And if you had it sitting on a cold surface you could have some temperature stratification of the electrolyte.

If you don't have such a charger then buy one -- for $30 it's a wiser investment than going towards a new battery. Or if you don't want to buy anything at least give the thing a few firm kicks to mix things up.

Check the case to see if it is bulging at all. If so, this is not good. Check the voltage after the battery has been disconnected for 8+ hours. If you have a hydrometer, even better.

I could go on and on... deep cycle batteries are my one obsession. Take care of the thing and it will serve you well.

 

OK, thanks for all of that information. If we may discuss your obsession further, what is the easiest way for me to determine the state of the battery at any given time, despite obvious stuff like bulges and such? For example, the battery I have (the one to the right) is rated to drive my pump for 7.5 hours. How do I know that my 3 year old battery still has the same ability to deliver something around its rated amp-hours at any given time, whether it's now or 3 years from now?

 

That's where things get really involved [time-wise] and you may or may not want to spend the time.

And I guess first it should be said that there's no guarantee that your battery really would have lasted for 7.5 hours even brand new.

I'm sure your battery lists the amp-hour rating on the sticker; the site does not. What I usually do to calculate the approximate amp hour capacity my batteries have left is:

- Let the battery rest, off the charger, for at least 8 hours to eliminate the surface charge.
- Get a voltage reading or hydrometer reading, and correct for temperature. There are plenty of charts available for this.
- Connect a known load to the battery and run it for a specific number of hours.
- Again, let the battery rest for a few hours with no load
- Get your final voltage or hydrometer reading

So now you know your starting and ending voltage, and you also know the amp hours you have actually used because you used a known load. For such a crude test you can assume that the voltage drop will be fairly linear as the battery goes from 100% down to 25%. (And you never want to run it below 25% state of charge if you can help it.)

We'll assume that 25% state of charge is 12.00 volts at your particular temperature. If you went from 12.8V to say 12.5V in 'x' hours then you can extrapolate how long it would have taken to get down to 12.0V. Multiply that by your known ameperage load, and that is your approximate amp hours while still having 25% reserve.

The faster you drain a battery the worse it performs. But I believe the Ah rating on the sticker is always based on a C/20 rate which is a moderately light drain on the battery.

Since what is more important to you is the actual sump pump time, (or if all of that is a bit much of a bother,) you could do some quick and dirty tests with your pump itself. Again, starting from a rested battery, run the pump for a specific amount of time and measure starting and ending state of charge based on temperature corrected voltage. If you went from say 12.8V to 12.6V in one hour of total pump usage then you can estimate that the pump would run for 4 hours before dipping into the 25%, or 5.33 hours total. Again that is just a very rough estimate but that is probably ok for your purposes.

Don't take voltage readings under load and always let the battery rest after charging or discharging before getting numbers.


Oh, and I wanted to add: Are you SURE that thing doesn't need water? I've seen plenty of people that don't refill theirs until the water level is down to the plates themselves. That is asking for trouble. Once the plates touch air that is not good.

And don't forget about that equalize charge. It could make a _world_ of difference, if you are not happy with your timed pump tests.

 

As far as the water level is concerned, I can sort of see through the case of the battery and can see the water level. There are also high and low fill lines on the case and the water level is exactly 1/2 way between the lines. The battery monitor also has an alarm that goes off if the level gets too low. In fact, I was sloshing around the fluid as you suggested and it was sort of chirping when the sensor was very briefly exposed during the sloshing.

That's interesting with the battery test. My only problem is that in order for me to test the pump, I imagine it would have to be under load during the entire test, and I just don't have that much water! And I don't want to run the pump that long without water as I'm pretty sure the pump uses the water for cooling as well.

I read about your equalize charge, but how do I do it? Just put the battery on a charger?

One last question.........considering that it could be really, really bad if this battery failed on me when I need it most, what is the longest time you would suggest I keep this battery without replacing it, especially if I can't perform your suggested tests regularly?

Thanks for your time,
ualdriver

 

Wow, that's a heckuva battery! Fluid level sensor and all. If the charge controller is equally as advanced it may be a lot more than a simple trickle charger. Maybe I could take a look at the manual on the site.

Yeah you defintely don't want the pump running for that kind of time. What I meant was total cumulative run time. I'm sure you don't want to sit down there with a stopwatch (but I have), so hmm....

In Chicago, you've probably got some snow over there. Which will start melting beginning of the week. What I'm getting at is maybe a time like this is a moderately heavy pump usage time? So you could let the run on battery power normally for say 4 hours. This won't tell you anything about how you compare to the 7.5 but you could probably extrapolate a good idea of how many days you have during these kind of conditions.

It also would be good for another reason: Get some juice running out of that battery after all these years. A shallow discharge, say to 75%, isn't going to hurt it any.

The charger you use must have an equalize setting on it in order to do it, and you will need to read the instructions as to how to activate it. It may be a very small hole that you need a pin to press, much like reset buttons on electronics. The point of this is they don't want you using it until you read the instructions and the warnings about hydrogen gas, etc. It will be a timed cycle and will actually "boil" the electrolyte in the battery.

The other thing I mentioned was a desulfate charge, which is separate. If your charger has it, it may be called desulfate, recondition, pulse, or really anything. This is a much longer process, can take up to 24-48 hours, and is not as agressive as an equalize. They are for totally different purposes. There is still an ongoing debate about how much it really helps, good arguments on both sides, but I do it religeously on all mine once a month.

My favorite charger that I use is a cheapo Vector VEC1095. Think it was $30-40 but it has all the features I just mentioned, and then some.

I think I'd be a terrible person to ask about that, since I refuse to throw any of mine away and keep a watchful eye and records on all my batts. They even have name tags. LOL. A battery is not going to go bad overnight. One way you can tell a battery has really gone south is if after charging it's showing a nice 12.8V but after just a few hours of rest it is already down a couple points, say 12.6V, causing the charger to activate again. If the charger is having to come on all the time then you know it's hosed. Even if I didn't have much free time on my hands I would feel comfortable with only doing a half-day on battery test maybe once every 6 months, once the battery is aged.

I don't know, for something this mission-critical it's just a judgement call. Anyone who gives you a fixed number of years is just making their own judgement call. If you never want to bother with the thing then sure you could just buy a new battery every 3 years. You could always keep the old battery too and have that much extra capacity, so it's not like the money would be a complete waste. If you think you're going to be home when the power goes out then you have nothing to lose by keeping a brand new battery _without_ acid in it stored somewhere. Then run the old one into the ground over many years. You've always got that spare.


P.S. Just noticed the 'UAL driver' and got curious, so looked at your profile and it confirmed my suspicions! Fixed wing VFR-only here. I'd sure have some questions for you!

 

Let me explain. I had a couple of 100Ah deep cycle gel cells in the boat. They were some 10 years old. I took a 50 watt edison base 12 volt bulb, bought at a marine store, put it in a test lamp socket, then put it across the battery, one at a time. Its very close to a 4 amp load. I timed it until the battery reached 11 volts. It took the better part of a day to do one battery. A new battery would hit about 24 hours, one that is "half good" is 12 hours, etc.

 

I don't know if this is possible in your case because I am not familiar with the pump itself, but possibly you could unplug the A/C and unhook the pump. Lift the pump out and place it into a big tub of water and hook up the battery power only. You could recycle the water back into the tub so it would just keep pumping. That would test the battery and the D/C section of the pump and give you a "real" answer to how long it will pump without A/C power. The motor should be rated for continuous use so I would think you could test it for as long as you wanted and find out how long you will really be protected.

 

Thanks for all that info core! I thing I'm going to purchase that charger and condition the battery as you mentioned. As far as your aviation/airline related questions, fire away!!

Thanks to the other posters as well. It wouldn't be an easy job to pull the pump out as suggested and recycling the water, but I think maybe putting a bulb or other load across the circuit or similar might be doable. I'm curious as to how this battery will perform actually.

Thanks all,
ualdriver

 

Unplug the main sump pump and let the backup work for a day or two, depending on how often it goes on. See what it does.

 

telecom_guy's bulb idea is very convenient, just keep in mind voltages under load are nowhere close to open circuit voltages. So you will need to use different calculations.

I would not drain any battery down that far. Under load, 11V would be about 5% state of charge under standard conditions. That's pretty darn low. Running it for about half that long would have been a little easier on the battery.

jn's water recycling setup is pretty clever. I had thought of mentioning something less elegant when I originally posted, but...

This is not an accurate test of your battery, unless the pump really will run constantly on a normal rainy day. Recall I said that the faster you drain a battery the less total energy it will deliver before it is dead. Running constantly, the pump may last 6 hours total. But when the battery has several minutes of rest time in between during normal off-and-on operation it may last 9 hours cumulative. Just hypothetical numbers here. Similarly, a very small light bulb will last for much longer than you expect even if you compensate for the exact amperage it draws. Just be sure to compare apples to apples is all I'm saying.

A nice light C/20 discharge rate is what you want if you're determining the amp hours of your battery compared to the amp hours listed on the sticker. telecom guy said his new one lasted for 24 hours so this was just about the ideal discharge rate.

I suppose since this is your thread a little off-topic question wouldn't hurt.

This one has been bugging me for _years_ and I've never found an answer. It has to do with jets "winking" on short final.

Are the port/starboard landing lights independently controllable on the big boys? Any reason they would intentionally "wink" one in such a manner when on final? I have seen this many many times so I can rule out a loose wire.

Only thing I can come up with is they might do this when approach is telling another aircraft to look for them. To temporarily give the other guy a better chance to report traffic in sight. But nah that doesn't even make much sense.

Maybe I'm just crazy. But I've had witnesses too! It could be an optical illusion, very dense but small clouds, etc. If the lights cannot even be controlled in such a manner then that would certainly settle it. Nothing I've ever flown had two switches.

 

I think testing the battery under the load of the pump is not practical for me, anyway. I think I'm going to invest in that charger and go through the process you mentioned and just replace the battery every 5 or 6 years. I appreciate all of the information you guys provided for me.

As far as the "winking" landing lights, you're not going crazy Some airlines and business jets have their landing lights on a circuit that alternates their left/right landing lights. From what I've read, they do it for two reasons. One, it's supposed to make the aircraft more visible in the sense that a alternating light in the distance is more noticable to the human eye than a steady light. Two, it was "supposed" to prolong the life of the landing lights, but I don't think it worked out that way as our airline stopped doing it because it wasn't prolonging the life of the bulbs. I think Southwest Airlines and a few types of business jets still do it as it is not uncommon to see those alternating landing lights now and then.

ualdriver

P.S. we don't use the terms port/starboard..........that's for boats

 

Hehe yes, yes, I know, don't give me a hard time. Don't even know why I said that. I guess I have had boats on the brain as my buddy's buying a houseboat this week. Maybe they'll teach me those complicated words like 'left' and 'right' during instrument training. *grin*

I think I've seen what you're talking about with the alternating lights, and this wasn't it. Both lights would be on at first as usual, and then the right right would go off for maybe a full second and then back on. (Other light remained on the entire time.) Nothing else would happen during the whole approach.

I live directly underneath the approach to DSM's 13L -- maybe I'll have to capture some video. The light simply being obstructed by clouds is sounding more likely now.

 

He-he......sorry for the slight thread hijack guys.........

Outside of what I mentioned above, I'm not sure what would cause that effect. It's possible, as you mentioned, that the pilot was manually flashing his landing lights to gain someone's attention, but that doesn't happen too often. Occasinally when we're at cruise altitude and we see another aircraft passing by, we'll flash our landing lights at each other as a little "hello" and just so we see each other when ATC points us out to each other. We don't do that very often in the terminal area.

Good luck with your instrument rating. When I was a flight instructor, I used to highly recommend that my students obtain an instrument rating as soon as they could, even if they never plan on flying IFR. It will make you a MUCH MUCH safer pilot.

Thanks for all the information you game me. Feel free to post if you have any more questions, too.

ualdriver

 

So, were you able to test your back up for a couple hours by unplugging it?

 

Could it be something as simple as the wings or flaps dipping on approach to mask one, then the other? I'm a (reformed) runway watcher.

To bring it back slightly on topic ... there have been two deep cycle 700AH marine batts in my boat for 20+ years. Not the same batteries -- I've had to change them out as they die off. I seem to get about five years out of each battery no matter if I trickle them in the garage during the off seaon or just let them sit. Both (and either) are switched, used as starters, and as dockside stereo power. Nothing I do seems to make them last longer than 5 years.

To be fair ... at roughly $80 each I'm pretty happy with five years of use life.

 

I think you meant 70, not 700. I would certainly not be able to lift a 700 AH battery myself. But if they really are 700's, I'd love to buy a bunch of those for only $80!

Are they actually rated for starting? If so they may be dual purpose rather than true deep cycles. I would not use a _constant_ trickle charge on any battery, and what about when it's not the off season? You just let them sit in the boat and let the boat charge them somewhat?

Often times it is a single cell which causes people to replace the things. An equalize usually fixes that.

Ah well, for $80 you can't complain if they last that long without fussing over them.

 

700 CCA. After a bit of searching, I believe they must be hybrids and not true deep cycle. Ummm ... it's also been about five years since I bought one for $80. I guess the price went up a bit ...

 

hi,
how is your battery now, does it still working ?

if so, check the battery terminal voltate see if it is still over 12V
Actrually, battery life is based on the plates and electroylet
for plates , deep cycle battery can supply more than 10 years
however. the electrolyte won't stay so long, so add pure water into the battery will help prolong the battery life

Besides, as time goes on. the battery capacity will decrease which means the backup time for the battey discharge will low and lower