Replace one battery in a bank?

searaycruisn

searaycruisn

New Member
Nov 10, 2006
242
Old Saybrook, CT
Boat Info
2000 380 Sundancer
Engines
CAT 3126
One of my engines was slow cranking (diesel 3126 - two batteries for each engine). I disconnected the batteries, and checked each individual cell in each battery using a hydrometer.

I only found one bad cell out of all of my batteries. I only replaced that one battery, and left the others in the boat.

Is this a bad idea? I have heard that you should replace all batteries in a bank, but is that am I just wasting money if the cells check out good with a hydrometer? Should I replace the other battery in that bank?
 
searaycruisn said:
One of my engines was slow cranking (diesel 3126 - two batteries for each engine). I disconnected the batteries, and checked each individual cell in each battery using a hydrometer.

I only found one bad cell out of all of my batteries. I only replaced that one battery, and left the others in the boat.

Is this a bad idea? I have heard that you should replace all batteries in a bank, but is that am I just wasting money if the cells check out good with a hydrometer? Should I replace the other battery in that bank?
Click to expand...
I have always replaced both batteries as a rule. I have tried to get by with only replacing one and it has never worked for me. I'm pretty sure the batteries have to be real close. They sell a load tester at Harbor frieght pretty cheap. That's what I would use to check them. If they are close you might get by with it.
Jack
 
searaycruisn said:
I only found one bad cell out of all of my batteries. I only replaced that one battery, and left the others in the boat.

Is this a bad idea?
Click to expand...

As you said, the "rule of thumb" is that you should replace all of them. But more importantly, make sure that you replace any/all with the same battery type. And preferably, the same manufacturer & model number.

I'd imagine if your other batteries are pretty new, it's no big deail to replace one. Otherwise, your others might be ready to go too.
 
I figure when one goes, the others are not far behind assuming they were all new at the same time. It's easier to do things on your schedule than to deal with annoying issues that pop up. I'm just now looking at batteries for my boat, getting part numbers and sizes. Mine are 5 years old and going strong. They are supposed to last 7 years, but when one goes bad they will all be gone. Hopefully that will not be for another 2-3 years.
 
You can't anticipate when a battery will go bad. Some will last 8 year, while others are done after one season. Replacing one battery is fine as long as you keep an eye on the other ones on that bank. I find that batteries are stupid boxes with lead in them. They don't know where they are and they don't know who there neighbors are. Keep the levels up, don't leave them on charge when you don't need to, keep the area clean and when in doubt , swap it out.
 
The battery banks are isolated, individual batteries are not.

So if you replace one dumb box of lead in a 2 battery bank, what happens when the older battery needs 14.4 volt for 6 hours to recharge it to 100% and the new one needs 13.6V for 30 minutes?

They don't need to know their neighbors, but when they are all in the same bank, the converter/charger cannot discern or taylor the charging need to individual batteries. Do it your way, and you will cook the stew out of the new battery, shorten its life considerably and at the same time, increase your cost of operation.
 
Check out the Charles SP 2000 charger.
Also the Newmar PT25 charger. Rated #1 and #2 in powerboat reports.
They monitor each battery, Switches for battery type, Read temp, Cut back to a float mode as needed.
They also work as a DC power supply.
Good for me when I get a portable generator :wow::grin:
 
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