Battery Failure from Deep Cycling.

[George7941]

I am trying to learn about how batteries fail when they are SLI(starting/lighting/ignition) batteries and they are deep cycled.

Vehicle in question is a Freightliner truck at work. It has two size 31 batteries in parallel (12v system) and a hydraulic lift gate at the back with the hydraulic pump run by a 12v motor. The liftgate draws about a 120 amps and it is used a fair bit, so it leads to some deep cycling of the two batteries.

The SLI batteries last only two years and then they are replaced. I just replaced them last week.

Deep cycle batteries are expensive, I think it is more cost effective to just get the cheaper SLI batteries and replace them more frequently. This time I got Dual Duty batteries(they are half way between SLI and Deep Cycle) and, hopefully, they will last longer.

I have the old batteries that I just replaced sitting in my garage. I fully charged them up and they could maintain 9v(and more)on a 100amp load for only about two minutes and then the voltage drops rapidly, so they are obviously at the end of their life. Here is something puzzling. I checked the Specific Gravity of the acid and it is 1.125 in one and 1.126 in the other!

I am trying to come up with an explanation for the high acid SG in the failed batteries. I believe when SLI batteries are deep cycled the plates are stressed and they shed material. If they shed lead and not lead sulphate, then I can see the SG staying high.

There is also a brown growth that is visible on top of the plates. It looks like dough but it is hard. What is it?

I have a Midtronics PB200 Conductance tester and it always shows these batteries as having full CCA even at the end of the batteries' life. This tester does not seem able to catch this kind of failure.

 

[Chris142]

Are these batteries the same ones that start the truck? I have never seen a truck with only 2 batts. Either three 1000cca ones or four 750cca ones.

The minimum cca is usually 1800. Add in some cold weather or a lift gate and they will be overstressed and die prematurly.

Can you plug it into a charger when not being used? I bet it's pretty hard on Alternators too?

 

[Scimmia]

http://www.batteryfaq.org/

Especially see chapter 16.

 

[George7941]

The same two batteries start the engine. Truck is a 1999 FL70 with the 5.9l Cummins ISB engine. It came from the factory with two 750cca batteries. Our 2004 Freightliner came with three batteries.

I have been replacing them with two 1000cca batteries. The parts guy mentioned that, under some circumstances, the 750cca batteries will last longer than the 1000cca batteries.

Our trucks are parked in a yard with no electrical supply available. Hence no way of using a battery charger or a block heater.

Chapter 16, referred to above, deals with sulfation. I don't believe sulfation is the problem here because of the high SG readings.

 

[alreadygone]

For service your describing in your cold winter climate,,I'd expect 2 years to be a good lifespan even without liftgate.

Bob

 

[Scimmia]

alreadygone, why is that? Heat kills batteries, cold temps will actually make them last longer at the expense of them being less active, so they can't deliver as much current.

George, you may be right, I was mostly answering the question about what kills starter batteries when you deep discharge them. From what I'd found with a couple of searches, though, that reading isn't that high, but doesn't point to sulfation. What temp were you testing them at? I know temp can have an effect on SG readings.

 

[brianl703]

SLI batteries have plates that are "spongy". This results in more surface area so the battery has a higher cold crank amp rating, but also means that the battery cannot be heavily discharged without damaging those plates. If the battery is heavily discharged the plates start falling apart--pieces of the plates fall to the bottom of the battery.

 

[Chris142]

Are they Exide batts?

 

[SHOZ]

1.125 is rather low SG. I would expect at least 1.250 on a fully charged battery.

The low SG would mean the sulfate ion is not being put back in solution. Sounds like the plates have sulfated and are junk. FWIW plate sulfation comes mainly from incomplete re charging or leaving a battery in a discharged state.

 

[George7941]

Error, Error! My SG readings were 1.25 and 1.26, not 1.125 and 1.126 as I had previously posted. They fall in the green(good) range of the hydrometer. The markings on the hydrometer were a bit misleading, 1.25 ia actually marked as .125.


"What temp were you testing them at? I know temp can have an effect on SG readings."
The temperature was about 18C, about 65F.


"Are they Exide batts?"
The old batteries are East Penn batteries, sold under the Alliance(Freightliner) brand. The new dual duty ones, branded Traction(Napa), are also East Penn.

 

[George7941]

I took a couple of pictures with a cellphone camera of the brown growth on the plates. Here is the link

http://good-times.webshots.com/album/562609722ZolDzu


It is not of very good quality but it was the best I could manage.