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Off topic battery question

S

slauder

Regular Contributor
House batteries. Have two deep cycle group 27 diehard same vintage (3 years old). Both tied together in parallel when in use. Both disconnected the winter. One read 11.2 and other read 12.6 this spring. I charged the low one and after two days it read 12.8. Could it be okay? Also any thoughts why one would be lower than other if they charge from boat the same way?
 
Not uncommon to have two same vintage batteries and have a cell in one weaker than the rest of the cells in the same battery. Two late now but if that same battery goes 'down-hill" put a meter on each cell when the battery is reading low and see if you have a weak cell.
 
3 years old and left with no trickle charge or care during the winter and showing signs of it..either replace them now or do it on emergency basis soon...you also need a ''splitter'' if in parallel to keep the weaker battery from sucking the strong one down if a partial short occurs..no two batteries will be equal for the duration of their life..
 
Going back to original question about unequal voltage on parallel batteries, do you have the positive and negative load connected to posts of the same battery? Doing so can cause more load on that battery than the other. Take a look at this link:
http://www.pbase.com/mainecruising/installing_a_marine_battery_charger&page=2

and this link with the picture in post #6 with the description just above in #5:
http://www.forestriverforums.com/forums/f218/wiring-two-batteries-together-question-34308.html

Dan
 
Not sure if this is relevant, but.... My good (and late) buddy convinced me that EVERY battery in a vehicle needs its own dedicated charger. The only exception is batteries in series (like two, huge 6 volt deals used to power a 12 volt inverter).

On my old boat, 5 batteries each had their own charger.

Jeff
 
...........................

Slauder said:
House batteries. Have two deep cycle group 27 diehard same vintage (3 years old). Both tied together in parallel when in use. Both disconnected the winter.
One read 11.2
A battery @ 11.2 volts is failing quickly and/or is DEAD.

and other read 12.6 this spring.
12.6 volts indicates a fully charged battery.
If the 12.6 volts can be maintained for 6 to 8 hours, this battery is likely OK.

I charged the low one and after two days it read 12.8.
Unlikely!


Also any thoughts why one would be lower than other if they charge from boat the same way?
Bad cell!
Low Electrolite level!
Non-distilled H2O being used.
Click to expand...

fastjeff said:
Not sure if this is relevant, but.... My good (and late) buddy convinced me that EVERY battery in a vehicle needs its own dedicated charger. The only exception is batteries in series (like two, huge 6 volt deals used to power a 12 volt inverter).

On my old boat, 5 batteries each had their own charger.
Click to expand...

Jeff, when putting together a HLBB (house load battery bank), all batteries should be of same type, same chemistry, same age, same group number, same brand, etc.... and whether 12 volt in parallel, or 6 volt in series.

Equally important, these should be Deep Cycle batteries, not hy-brid dual purpose, etc...... Real Deep Cycle batteries!

Unfortunately, we cannot guarantee ourselves that each of these batteries will perform identically.

However, they should all remain in this bank, and should be called upon for AH as a bank, and should be charged as one large battery bank.

If one cell begins to fail...... hopefully we'll catch it.


.
 
Trust me: NO two batteries--even if they are 'identical'--charge the same. And when they age, the differences increase.

It cost me lots of $$$ to find this out.

Jeff
 
Jeff, I understand you.
However, the switching that would be necessary for HLBB use, for isolation, for separate charing, etc..... would prevent most of us from doing what you suggest. It would simply be too complex to be practical.

Grouping batteries for a HLBB has been done for years and years.
I myself have been doing this for years, although I use 6 V GC batteries in series for the additional Amp Hour capacity.

If/when I were to have an issue, it would most likely be from a faulty battery cell.



.
 
---"I myself have been doing this for years, although I use 6 V GC batteries in series for the additional Amp Hour capacity."

THAT will work fine. It's when a bunch of them are in parallel; that's when trouble starts.

Jeff
 
Please, if you decide to replace ur battery, replace them both, putting a new battery with a older battery will rob the new battery. If you have the room, I'd go to group 29's or even 31's with the highest reserve amps you can get. It's a tough to get a jump start out in the middle of the lake.
Mike
 
mjk1040 said:
Please, if you decide to replace ur battery, replace them both, putting a new battery with a older battery will rob the new battery. If you have the room, I'd go to group 29's or even 31's with the highest reserve amps you can get. It's a tough to get a jump start out in the middle of the lake.
Mike
Click to expand...
If we are speaking about a HLBB (house load battery bank), the 6 volt Golf Cart batteries (in series) do an excellent job providing AH for this purpose. We can do 2 or 4 or even more.
While being grouped "in series" doubles our voltage (6 v becomes 12 v), we do not get to double our AH, but these generally begin with a greater AH capacity than that of similar sized 12 volt batteries.

fastjeff said:
... and be sure they have a dedicated charger, one per battery.

Jeff
Click to expand...

Jeff, all due respect ..... but I believe that you had/have an unusual scenario re; your grouped batteries.
Many of us group our "like" batteries as to form our HLBB and do not have the issues that you've spoken about.

 
A designated charger is the answer..
Two 12V in stern...connected in series for Thruster...each battery has it's own charger
Two 12V in bow....connected in series for Thruster...each battery has it's own charger
Two BIG RED House batteries connected in parallel..each with 3 solar panels per battery.. 900 watts solar per battery
House bank runs through 3000 watt Pure Sine Wave inverter... Everything that can be,(even the AC Fridge) has LED bulbs etc.
Each engine has it's own charger ...from Alternator
Genset when required uses two engine batteries (if required...normally only one) to start

Been working well for 3 years now.
 
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