Is 12 volts 12 volts?

2-6volts(7Ah) rechargeable batteries in series...hooked in parallel,with a 12volt(120Ah) deep cycle battery.
First question.
Is there now 127 amp hours?

Next,when they need recharging,
can they stay in parallel(like they are)and be charged with one charger?

Could you use the 10/15amp charge rate because,it's 127 Ah's(10-15% rule,if there is one) or would you have to trickle charge them because of the 7 Ah batteries?

Lets say all batteries are new and not faulty,weak or with any other defects.
This isn't used for anything...just wondering.
I was going to ask about 8-1.5V batteries in series,hooked parallel with a big deep cycle.

I'm thinking 12 volts is 12 volts,am I wrong?

Re: Is 12 volts 12 volts?

12 volts is 12 volts is a very true statement. Doesn't matter if the battery is a 7AH or 120AH. You have an issue however in that those two 7AH batteries require a much lower charge rate than the 120AH. Usually less than 2A so you would likely cook them at a 10-15A charge rate. Next question however, is why add those two small batteries to a very large (in comparison) battery? The added capacity is very little more than 5% and hardly worth the trouble. If you were talking about two golf car batteries in series and then paralleling them with a single wet cell then yes - that would be a workable system. Yes - 8, 1.5 volt batteries in series is 12 volts but a wet cell is 12.6 volts. Again -- why even think about this since alkaline batteries cannot be recharged and would likely pop when connected to a big wet cell. NiCads and NiMH are both less than 1.5 volts per cell. Just wondering what your logic is in all of this.

Re: Is 12 volts 12 volts?

Your 12V lead acid battery is actually 12.6V fully charged. Different chemistry batterries have different fully charged voltages. You can't hook different chemistry batterries in parallel or the one with the lower fully charged voltage will get overcharged.

Re: Is 12 volts 12 volts?

This is just for general information.
Like said in the previous post..."This isn't used for anything,just wondering."
I don't like saying never but I don't think I'd ever try this example.
Although it would be kinda cool to see 2-7Ah batteries,last a real long time hooked to a trolling motor.(if in parallel with the 120Ah)

Real reason why I asked...
I guess wondering because often I hear(read) of people wanting to use a good 80Ah battery,with a bigger 150Ah battery.(both 12V,like a group 24 and a group 31).Alot of people comment or say don't do it,it's bad,it's going to blow up,etc,etc...
As long as both batteries are good,I don't see the problem.
Even if ones alittle older then the other but still concidered good,I don't see something catastrophic happening.
The better battery(higher voltage) will settle out and take the voltage of the one thats alittle lower,if left in parallel.
Again I'm talking about good batteries,not ones with a bad cell or really weak...

Maybe I should of asked about a starting battery and a deep cycle together,in parallel just for charging.

BruceB58...now I wonder what the + - is,on batteries when charging?
We all know batteries often get over 12.6V,when charging or hooked to an alternator charging circuit and fall below that number,sometimes when discharged.
I asked this because you have me wondering if say a 12.9 volt battery,should be hooked together with a 12.6 volt battery.
I thinking,it's not any problem...am I wrong?
There in parallel(both 12V),from what I've read and makes sense to me,the higher voltage battery,will level out to the voltage of the lower voltage battery after awhile.
I say again,both good 12 volt batteries but maybe not exactly the same when fully charged.
Wonder what the percentage is...

Re: Is 12 volts 12 volts?

pootnic said:

Real reason why I asked...
I guess wondering because often I hear(read) of people wanting to use a good 80Ah battery,with a bigger 150Ah battery.(both 12V,like a group 24 and a group 31).Alot of people comment or say don't do it,it's bad,it's going to blow up,etc,etc...
As long as both batteries are good,I don't see the problem.

Click to expand...

I agree. Nothing is wrong with using different size or type batteries in parallel as long as the voltage is the same. They should perform fine together. If they are not matched well, however in the long run you will find that battery life of the smaller battery will be shortened. I think the most important risk is when charging. They should be charged separately and at their optimal rates. Charge them separately even if they are supposed to charge at the same rates. Two reasons: 1. because diff size batteries even of the same type will have differing charging times. 2. charging two batteries will require twice as long at a given Amp setting or you will have to up (double) the Amp setting and hope that the smaller battery doesn't charge too fast and overheat. If the batteries are closely matched and charged together you may never notice a problem, but the bigger the differences between the two batteries the more this will effect the overall performance and life. Hope this helps.

Also, always jump the smaller battery over to the bigger one then pull your load from the bigger one. This ensures that the little one doesn't get drained if your jumper connections between the batteries fail or become less conductive.

Re: Is 12 volts 12 volts?

I would never connect batteries in parallel or series unless they are virtually identical. Even their age will change their discharge and charge rates. Since this is an academic question, have a look at this website. If you look at the root of the site you'll find a fantastic amount of free info. - Grandad http://openbookproject.net//electricCircuits/DC/DC_11.html

Re: Is 12 volts 12 volts?

pootnic said:

BruceB58...now I wonder what the + - is,on batteries when charging?
We all know batteries often get over 12.6V,when charging or hooked to an alternator charging circuit and fall below that number,sometimes when discharged.
I asked this because you have me wondering if say a 12.9 volt battery,should be hooked together with a 12.6 volt battery.
I thinking,it's not any problem...am I wrong?
There in parallel(both 12V),from what I've read and makes sense to me,the higher voltage battery,will level out to the voltage of the lower voltage battery after awhile.
I say again,both good 12 volt batteries but maybe not exactly the same when fully charged.
Wonder what the percentage is...

Click to expand...

A lead acid battery will have a voltage of 12.6V +/- a very small voltage which varies by the age of the battery and a few other characteristics. The voltage that the battery gets charged at means nothing to what the steady state voltage of the battery is when it is fully charged. Not sure where the 12.9V comes from. When you measure a battery after it has been charged, you need to let it sit for 30 minutes before measuring it. This allows the surface charge to dissipate.

Re: Is 12 volts 12 volts?

toy4x4 said:

hope that the smaller battery doesn't charge too fast and overheat.

Click to expand...

Won't happen. As a battery charges it demands less charge so if you charge two batterries in parallel and one is more charged than the other , the one needing the charge will automatically get the current.