2 volt batteries

bottom_dweller

Active member
I just replaced a set of 12 v batteries for 6- 2 volt batteries. I have always charged the 12v to 13.5-14 volts. My question is do I charge this bank to the same voltage or should I charge these 2 volt batteries different when connected up to make 12v?

Patsfan54

Well-known member
What you've done is go from a single cell battery to a multicell battery or battery bank, at the end of the day as long as you've hooked them up correctly you have a 12 volt battery so you charge them the same.

MacGyver

Well-known member
Details matter:
If you don’t care about losing performance ( Amp-hours) because they are not balance? Yes, you can put them in series (12 V) and charge them. Or you can buy batteries that have the same manufacturing date. Put them ALL in parallel ( 2 V ) and charge them per the manufacture recommendation.

When in doubt ask the manufacture.

iofthetaiga

Well-known member
You can charge to 13.5 or 13.8 or whatever at the top end, depending on exactly what the indvidual voltage of your "2" volt cells is, but what's potentially more important is how you get there. Be sure you're up to speed on the various implications of cell imbalance within the series string. Besides reduced cell life / amp hour performance over the longer term, there is potential of putting individual cells in a severe overcharge state, and potential implications toward what type of charger you choose / how you go about charging the string.

To address your specific question we need to understand that most common "12 volt" FLA batteries are actually ~13.8 vdc batteries with an approximately 12 vdc float, and we refer to them as 12 volt batteries. If your individual cells are actually 2.0 vdc, then you would charge a 6 series string of them to 12 vdc. if they're actually 2.14 or 2.2 vdc (which is the case for most typical "12 volt" FLA batteries), then you multiply that by 6 and charge accordingly.

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bottom_dweller

Active member
We picked these up many years ago 6-8 maybe. They are a bolt together design that bolt 3 2volts together and then there is one jumper to connect a positive and negative together for 12v. We got busy with life and they just sat out not bolted together or used. When our old ones bit the dust I installed but just wondering about the condition and how much to charge. They are definitely better than what I took out but not coming up very fast.

iofthetaiga

Well-known member
We picked these up many years ago 6-8 maybe. They are a bolt together design that bolt 3 2volts together and then there is one jumper to connect a positive and negative together for 12v. We got busy with life and they just sat out not bolted together or used. When our old ones bit the dust I installed but just wondering about the condition and how much to charge. They are definitely better than what I took out but not coming up very fast.
That doesn't sound like series. That sounds like a series / parallel combination. There are different possible ways and implications of charging a series / parallel combination bank. You should research that, at least for background knowledge.

Also, given they've been sitting for a long time it's likely they're in various states of discharge. Hopefully none of them has fallen below the minimum for charging (you'd probably know by now because the series would probably refuse to charge at all...). If it were me, and I had the ability, I would fully charge them individually to their 2 vdc float before connecting them in combination, to mitigate against individual cell imbalance while charging them in combination. If not, hopefully you're using a lower amperage "smart" pulse type charger, that will bring them up gently over 12-24 hours. That's better than hitting them with a fast charger.

The cell imbalance issue can be thought of similarly to filling a series of fuel tanks connected with small cross feed lines. You fill the first tank with the high flow nozzle, but the downstream tanks don't fill at the same rate, and you overfill the first tank long before the others are filled...and with batteries, that makes them very unhappy.

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bottom_dweller

Active member
If it were me, and I had the ability, I would fully charge them individually to their 2 vdc float before connecting them in series, to mitigate against individual cell imbalance. If not, hopefully you're using a lower voltage "smart" pulse type charger, that will bring them up gently over 12-24 hours. That's better than hitting them with a fast charger.

The cell imbalance issue can be thought of similarly to filling a series of fuel tanks connected with small cross feed lines. You fill the first tank with the high flow nozzle, but the downstream tanks don't fill at the same rate, and you overfill the first tank long before the others are filled...and with batteries, that makes them very unhappy.
Thanks for that. I don’t have the ability to charge each individually but I am bringing them up slowly (days).. I think 3 now and we’re at 12.7. 11.2 was the starting voltage.

iofthetaiga

Well-known member
Thanks for that. I don’t have the ability to charge each individually but I am bringing them up slowly (days).. I think 3 now and we’re at 12.7. 11.2 was the starting voltage.
OK. And I take back the first thing I said above. It is series, because you're achieving 12 vdc from six 2 vdc cells; all the bolt together cells must be connected positive to negative; two banks of three each are then connected with a longer jumper positive to negative (for physical space configuration purpose, rather than having all six bolted up in a single long row). Thing is, that longer jumper itself creates potential imbalance implications during charging and high load discharge; typically with banks it's highly desirable to keep all the connecting jumpers exactly the same length... It's worth doing some reading up on such things. Good you're bringing them up slowly. Once you're done charging, it would be good to unbolt them all and put a meter on them individually to know if you have any unhappy individual cells.

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Patsfan54

Well-known member
It all depends on the design and how they bolt up whether they are series, parallel, or series/parallel. If all the cells bolt positive to negative then they are in series and you have a 12v battery system, which is what it sounds like you have.
If all the positives are bolted together and all the negatives are bolted together then they are in parallel and you have a 2v battery system. If 3 cells are bolted together positive to negative in one group and the other group of 3 cells are bolted together the same and then the positives and negatives from both groups are bolted together then they are series/parallel and you have a 4v battery system. If 2 cells are bolted together positive to negative in three groups and then the positives and negatives from each group are bolted together then they are series/parallel and you have a 6v battery system.

Did you check the voltage of each cell before charging or just the group as a whole?

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bottom_dweller

Active member
It all depends on the design and how they bolt up whether they are series, parallel, or series/parallel. If all the cells bolt positive to negative then they are in series and you have a 12v battery system, which is what it sounds like you have.
If all the positives are bolted together and all the negatives are bolted together then they are in parallel and you have a 2v battery system. If 3 cells are bolted together positive to negative in one group and the other group of 3 cells are bolted together the same and then the positives and negatives from both groups are bolted together then they are series/parallel and you have a 4v battery system. If 2 cells are bolted together positive to negative in three groups and then the positives and negatives from each group are bolted together then they are series/parallel and you have a 6v battery system.

Did you check the voltage of each cell before charging or just the group as a whole?
No I didn’t check the voltage before bolt together. The way they bolt together was very intuitive. The bolt up tabs had letters to correspond with each other. 6 in series is what the end result is I believe. The jumper is two feet long and 2/0 cable. Not wimpy. I know I have them hooked up right or my meter wouldn’t read anywhere close to 12v. I am hoping to salvage them as everything seems to have quadrupled in price since I bought them.

Patsfan54

Well-known member
If it hasn't risen above 12.7v by now then that's probably all you're going to get out of it. It would be worth doing a load test on it to see how it performs, if you have one bad cell it shouldn't take long to find out if it's bad.

bottom_dweller

Active member
If it hasn't risen above 12.7v by now then that's probably all you're going to get out of it. It would be worth doing a load test on it to see how it performs, if you have one bad cell it shouldn't take long to find out if it's bad.
All seems good. Turned off the genny last night and the voltage was at 13.8. Now I need a smart charger.

tvfinak

Well-known member
For battery banks of any size check the individual cell voltages at rest, charging, and under load. Individual bad cells will show up quickly, and one bad cell can mess up the whole banks performance. Even maintained as a group, individual cells will fail before the others.

Sitting inactive for long periods is not a good thing. Put a load on the occasionally, and check performance. There were a lot of problems with batteries for the pieline rebuild because the replacement batteries sat unused for a long period of time before installation.

There are scores of battery banks on the North Slope and pipeline for emergency power. Testing and maintaining them has always been a major chore. Most have went now to sealed jell cells to avoid the issues of the acid in flooded cells.

Akgramps

Well-known member
I didn't read all the replies, so apologies if this has been said.
If they are flooded batteries, make sure they are topped up and I would do a equalization charge to each battery separately if they have been sitting.
You can evaluate there condition by checking specific gravity in each cell.

Your charger needs to be sized to your bank in terms of amps. If charging individually then you need a charger for a 2V battery, if charging the 'bank" then you need the appropriate voltage for that bank.

If it were me I would want to make sure each battery was fully charged and able to provide the amps it should, if one is weak it will detract form the others.

I would contact the manufacture of the batteries and ask them some specifics.