Don't have my references handy so over to you guys please. If you have a good and bad 6 in series will the bad one ruin the good one? (Where the combo still acts ok as a 12 and is working ok for discharging and recharging)I know about the parallel situation where one drags down the other etc. But what about in series?Actual situation-- six-year old pair of 6s. When "full" one has three cells just in the green and the other has the middle cell just in the green but the outer two are in the red on the hydrometer.Is it just like a single 12 with six cells in series with two low cells?If the bad one won't ruin the good one, is it safe to add two more old 6s (both good) to have four in series/parallel? Will the pair with the bad one ruin the good pair it is in parallel with?If so, is this ruination a slow process --months? or fast--weeks?Thanks

When I had my bad interconnect cable the low SG 6V was continuously pulling amps from the Iota. Not much amps as they were on float but still pulling. It didn't seem to have much effect on the high SG 6 as it was only a little lower in SG than baseline. That could've been because I caught it early. Long term might have been different.

Hi BFL13,No the series connection will not "ruin" the other six volt jar--but capacity will be limited to what ever the worst "bad" cell can produce.You might try getting "fancy" and equalizing just the one cell by using a probe and a 2 volt charging current.Adding another series string won't help and would drag the "good" sixes down in capacity to what ever the worst cell does.

The capacity of the combo now with the one bad battery has not been measured. It will accept draws of over 100amps to run a microwave or toaster. When resting at 12.6 it will hold at 11.5 for two minutes with the microwave on, which seems fairly sturdy for a bad combo IMO. (U-2200s)Based on that, the owner is not going to be panicked into buying new batts just yet. I have advised him (he agrees) to try to last until end September when the trailer will be stored until next April. If he can hang on, then he can buy two or four new 6s next April and have no batts to maintain all winter, tossing these in October.The question really is what are his prospects with the good and bad 6s he has now? Three months to go. Does it happen that fast?(Back up plan is I can lend him a T-1275 or two to get him by if it all goes to poop.)

The bad battery, will limit the draw through both batteriesAnd will limit the amount of rechargeTotal capacity will be less than normalAnd the good battery will be slowly made worse, because of improper/Low recharge

Think about the issue with individual 2V cells. Parallel and series wiring attributes stay the same. Many of your 2V cells are already connected in series.

Series vs Parallel on Good and Bad Battery Combo?

14 Replies

MEXICOWANDERER
Explorer
Jun 27, 2014
Different construction. Different voltage characteristics. That's what will eat batteries resting in parallel.

No matter how it is expressed they are all six cell systems. Some are paralleled, others no.

Imagine me. One 3-1/2 digit fluorescent display. A 12 pole rotary break before make switch. Sip of coffee, click. Another sip of coffee, click. Lazy engineer's way to wake up. Click, click, click...

Dangit! Where did I see that 5-amp 30 volt power supply? I lost the url. I posted it here on this forum....
wa8yxm
Explorer III
Jun 26, 2014
BFL13 wrote:
Don't have my references handy so over to you guys please. If you have a good and bad 6 in series will the bad one ruin the good one? (Where the combo still acts ok as a 12 and is working ok for discharging and recharging)

I see many folks talk about the need for all batteries in a group to be IDENTICAL (Same, age, size, capacity, type, chemistery (Agm/Flooded) and so on.

This is true of batteries IN SERIES but read on for parallel.

In your case.. First thing i would try is an EQUALIZATION charge to see if that fixes it.. Then check your fluid levels (Set to 1/4 inch below filler tube or close to that, use DISTILLED WATER only to top off) and run a 2nd Equaliation charge.. This may fix it.

Else answer this question: Would you replace just 1/2 of a 12 volt battery?

The reason I say this, is you do not have six volt batteries in your RV, you have a 12 volt battery, which has been packaged in two halves for ease of handling (By the way its a 4D if you want to know it's size) 230 amp hours at 12 volts is the capacity of a 4D, or two six volt GC-2 in series.

But always replace BOTH HALVES when replacing a 12 volt battery (made up of six volt twins in this case)

Page 2

12 volt in parallel.

The need for identical everything is much overrated. I have at least 4 different 12 volt (5 actually) batteries in parallel

One six volt twin DEKA G-20's (A GC2 battery)
One Deka Group 78 starting battery (Chassis via a BIRD)
One I have no idea got it at Tractor Supply suspect it is an Excide
And two from Wal mart, Group 29's. All maintenance free (As is the 78) all different ages (Except for the DEKA's were within 3 months) the Twins are flooded wet cells of course.
mena661
Explorer
Jun 26, 2014
MEXICOWANDERER wrote:
Like asking where the kindergarten student with Ebola is supposed to sit...
LOL!
MEXICOWANDERER
Explorer
Jun 26, 2014
Suggestion...

Google KIRCHOFF'S LAW

Apply the rules of current (amperage) flow through a series of battery cells.

Good Battery / Bad Battery

Like asking where the kindergarten student with Ebola is supposed to sit...
ken_white
Explorer
Jun 26, 2014
RJsfishin wrote:
No, it will not ruin the good battery.
It will be good till Sept, and probably a lot longer.
If you dint have that dam hydrometer, these questions would not even exist.
It won't be that much longer when batteries won't have any holes to poke a hydrometer in to, and all the battery fanitics will live a much happier life.
:)

So a bad cell in a 12V battery won't ruin the other cells or wreak havoc with the charging system?

A bad 12V battery paralleled with a good 12V battery won't prematurely wear out the good battery?

This scenario is no different...
RJsfishin
Explorer
Jun 26, 2014
No, it will not ruin the good battery.
It will be good till Sept, and probably a lot longer.
If you dint have that dam hydrometer, these questions would not even exist.
It won't be that much longer when batteries won't have any holes to poke a hydrometer in to, and all the battery fanitics will live a much happier life.
:)
ken_white
Explorer
Jun 26, 2014
BFL13 wrote:
Don't have my references handy so over to you guys please. If you have a good and bad 6 in series will the bad one ruin the good one? (Where the combo still acts ok as a 12 and is working ok for discharging and recharging)

I know about the parallel situation where one drags down the other etc. But what about in series?

Actual situation-- six-year old pair of 6s. When "full" one has three cells just in the green and the other has the middle cell just in the green but the outer two are in the red on the hydrometer.

Is it just like a single 12 with six cells in series with two low cells?

If the bad one won't ruin the good one, is it safe to add two more old 6s (both good) to have four in series/parallel? Will the pair with the bad one ruin the good pair it is in parallel with?

If so, is this ruination a slow process --months? or fast--weeks?

Thanks

A single bad cell in a 6 VDC to 12 VDC series connection will damage the good battery during charging since the overall battery voltage will be somewhat lower than 12 VDC.

The charging device will try to maintain a nominal charge voltage which means each of the good cells will receive an overcharge which will boil electrolyte and possibly damage plate material.

When you parallel the good string with the bad string, the good string will work hard trying to maintain 12 VDC while acting as a source - lots of circulating currents.

Battery life will be reduced for all batteries...
time2roll
Nomad
Jun 25, 2014
Just weak performance in series. Once you go parallel then the issues start. Depends on how bad is bad. Better to just get 4 new and move on.
dons2346
Explorer
Jun 25, 2014
If you have more than one battery tied together, the total package will be no better than the worst battery in the system. Don't mix good with the bad
westend
Explorer
Jun 25, 2014
Think about the issue with individual 2V cells. Parallel and series wiring attributes stay the same. Many of your 2V cells are already connected in series.