Battery Longevity

[John_Mc]

My bet is that one of your cells is shorted out or partially shorted. With the bad battery connected, you will probably see the voltage drop dramatically when attempting to start.

There are some problems that even a good quality desulfating charger cannot solve.

 

[Gregster613]

Yes John_Mc, that's what I believe happened. I just changed it for a new one from Napa (more pricey than I thought though). I'm going to try using the damaged, but not totally dead one, as a power source for my dc fuel transfer pump. Maybe I can still use it for awhile and maybe not. I will find out. Greg

 

[John_Mc]

Yes John_Mc, that's what I believe happened. I just changed it for a new one from Napa (more pricey than I thought though). I'm going to try using the damaged, but not totally dead one, as a power source for my dc fuel transfer pump. Maybe I can still use it for awhile and maybe not. I will find out. Greg

Not positive about this, but I've heard that charging batteries with a bad cell can cause problems - you end up overcharging the other cells until the charger either gives up, or sees that that battery is up to its expected voltage. The overcharging can cause out-gassing of Hydrogen Sulfide (H2S): a colorless, highly toxic, corrosive gas. Overcharging can cause the battery to burst as well, leaking, or even spraying battery acid all over the place.

If it has a bad cell, I'd be inclined to retire the battery. Using it in a situation involving fuel is probably not a great idea. If you really want to see if it has any useful life remaining, take it someplace that can thoroughly test the battery and let you know its condition. Most auto parts stores can do this, as can many auto mechanics' shops.

 

[Gregster613]

You're probably right John_Mc, it's not worth the risk of future problems by messing around with this battery. I'll just dispose of it and avoid causing anything else to go wrong. Trying to be frugal (cheap) isn't worth an incident. Thanks for helping me to think this through completely. Greg

 

[goeduck]

My bet is that one of your cells is shorted out or partially shorted. With the bad battery connected, you will probably see the voltage drop dramatically when attempting to start.

There are some problems that even a good quality desulfating charger cannot solve.

Not doubting just trying to understand. If one cell is shorted out, why would the battery come up to the correct voltage? I would think it would be 2 V low.

I would have guess stratified or sulfated

 

[fried1765]

You're probably right John_Mc, it's not worth the risk of future problems by messing around with this battery. I'll just dispose of it and avoid causing anything else to go wrong. Trying to be frugal (cheap) isn't worth an incident. Thanks for helping me to think this through completely. Greg

Good choice !!

 

[John_Mc]

Not doubting just trying to understand. If one cell is shorted out, why would the battery come up to the correct voltage? I would think it would be 2 V low.

I would have guess stratified or sulfated

Not sure how it happens. I think the charger just overcharges the remaining cells, since it is trying to bring the whole battery up to a certain target voltage. I had a battery that would measure about 12.4-12.5 volts when put on the charger overnight. When I tried to start the 12 HP engine, there was not enough juice to turn it over. If I charged it back up, and then disconnected the charger, it would measure about 10.5 V the next day. I later recharged the battery and measured the voltage while trying to crank the engine. As soon as the switch was turned to start, the battery dropped to 10.5 volts. Tested at a local auto parts store and they said "shorted cell". (I'm told a very heavily sulfated battery can short out one or more cells. If it's bad enough, a smart charger with a desulfation circuit will not be able to bring it back. That was the case with this one, despite trying for an extended period - with battery kept ousdie and away from anything it could damage if it burst.)

I've since purchased a load tester, so I can get a better idea of a battery's condition without bringing it somewhere.

 

[Grumpycat]

Not positive about this, but I've heard that charging batteries with a bad cell can cause problems - you end up overcharging the other cells until the charger either gives up, or sees that that battery is up to its expected voltage. The overcharging can cause out-gassing of Hydrogen Sulfide (H2S): a colorless, highly toxic, corrosive gas. Overcharging can cause the battery to burst as well, leaking, or even spraying battery acid all over the place.

If it has a bad cell, I'd be inclined to retire the battery. Using it in a situation involving fuel is probably not a great idea. If you really want to see if it has any useful life remaining, take it someplace that can thoroughly test the battery and let you know its condition. Most auto parts stores can do this, as can many auto mechanics' shops.

Not just an "I heard" but hard fact. One bad cell causes others to overcharge because the only practical means of limiting charge is voltage. The charging algorithm says, "I need to see 13.8V and I'm going to hammer it until I do."

This is a Mercedes-Benz Original Equipment Bosch AGM with a bad cell which M-B's much touted bad battery algorithm missed. Battery is under front passenger seat and is installed before the carpet. Carpet must be cut to access battery for the first time, has perforation, owner's manual says as much.

 

[Grumpycat]

Not doubting just trying to understand. If one cell is shorted out, why would the battery come up to the correct voltage? I would think it would be 2 V low.

I would have guess stratified or sulfated

The other 5 cells are forced up to 13.8V before the charging algorithm backs off. They get overcharged.

 

[LouNY]

Not just an "I heard" but hard fact. One bad cell causes others to overcharge because the only practical means of limiting charge is voltage. The charging algorithm says, "I need to see 13.8V and I'm going to hammer it until I do."

This is a Mercedes-Benz Original Equipment Bosch AGM with a bad cell which M-B's much touted bad battery algorithm missed. Battery is under front passenger seat and is installed before the carpet. Carpet must be cut to access battery for the first time, has perforation, owner's manual says as much.

View attachment 679702

That's the first time I've seen an AGM battery with corrosion on the terminals.