36V 12Ah Battery + 12V 12Ah Battery in a Series?

Depends if they are from the same manufacturer and have the same cell characteristics.

If so, there shouldn't be too many issues with charging them from a single 48V charger. The only issue will be the inter-cell wiring, as I presume the 36V and 12V batteries come pre-wired. Usually, you'd try to connect every cell in series so that the charging current flows through every cell evenly. But when you hook up two pre-wired batteries together, you'll introduce a parallel path, which will mean that some cells will likely be charged more than others. I'm not sure how you can resolve this unless you have access to the cell terminals.

Re: But when you hook up two pre-wired batteries together, you'll introduce a parallel path, which will mean that some cells will likely be charged more than others.

I don't see where there would be a parallal path, especially since these batteries will be wired in series to get to 48 volts, both in use and while charging?

Agreed, there should be no problem here. The critical issue is amp-hours of storage capacity. Since both batteries match it's all good. I assume these are gel cell batteries based on your description. Trickle chargers work best for these although they are a little slow.

Well thanks for the speedy replies the batteries are from 2 different places the 36volt is a monster battery and the other is from batterygeeks. They both are agm batteries and I used the pack for the second time and turned on the charger and it turned green after a couple hours. I didn't run down the batteries past half way. Should I have a volt meter and check each battery after they charge maybe.? I don't know very much about batteries only what I've read on the internet. The reason I combined the 2 batteries besides already having the 36volt is because the place I bought the battery said it was fine and seemed to be knolledgable but who knows.

A meter will only help if the batteries are under load. In other words, reading terminal voltage with no load is useless information.

Thanks well maybe only time will tell if it works out I'd do the same thing again. The 36volt battery is cheaper and smaller than 3-12volt batteries, less space less weight all good on an electric bike.Probably crash trying to check the voltage while riding the bike and would have to buy a volt meter as well.

Oops, yes you're both right. I was thinking about another case entirely! Forget I said any of that...

My opinion is must always use the same size and same batch of battery for series. this is because each battery internal resistance is different. If we series up 36V + 12V, the 12V battery will normally receive higher charging voltage at the initial charging stage because it has lower internal resistance compare to bigger size battery.

My experience is that series up 12V battery x 4 units to make up 48V for golf buggy, after certain period of running, the charging voltage per battery is different. The most positive battery will receive lesser voltage and most negative will receive higher voltage. This is because we drain the most positive side of battery and the last battery receive charge first. This means most positive battery actually drain up more than other first in sequence. When most positive battery having higher discharge rate, it means high internal resistance in that particular battery. Therefore, i have to get my maintenance team to swap the battery position every month in order to balance up the battery lifespan.

I am truly sorry to bug you here, but that is dangerous and misleading c**p!

I personally have seldom read such wrong & inaccurate infos in my whole damn life.

I am fully prepared to retract my comments made here if you can prove that your twisted explanation has any basis of real truth in it.

Except POSSIBLY the first paragraph of yours which although badly written, may actually contain some correct facts if witten better. No one in their right (or left ) mind would place a 12 volt battery across a 36 volt charger (if that is what you were implying, I am not really sure) and not expect to let the smoke out from something!

Where did you learn English? You dont say where you come from, but guessing I would say either just US grade school or English is not your first language, naturally it could be both of course!

So please either retract your complete statement or offer us links that support and explain your comments fully. NOT doing one or the other may leave a bad taste for many here.

Thanks in advance for clearing this mess up.

Everything you just wrote is incorrect.

I have to agree with other colleagues on CR4, what you have written here has absolutely no value whatsoever. The only good part is that the grammar is so bad, nobody will understand it either!

But stick around, read further, you can learn from others here.....

TIP:- never comment on something that you have basically no idea or training for.....only ask questions....

Best of luck for the future.

since they are both rated 12 AH there should be no issue. One of the other members brought up that there maybe as both are from different manufactures. The internal resistance may be different from one manufacture to another. This may cause one to over charge. To tell if you are going to have that problem. Place them on charge until fully charged. If you have a charger that shuts down after charge. Just turn it back on wait a few minutes. If it has amp meter on it until it settles. Then take a voltage reading on both batteries. You should not have more then 2.5 volts per cell on either battery. Taking the voltage drop on each battery and dividing it by number cells in that battery will give you that. The closer the cells are in there voltage drop from one battery to the other the better.

How would I know how many cells each battery has? They are sealed batteries.

If they are lead/acid batteries they should have 2.3 --> 2.4 volts/cell fully charged.

This is in line with a fully charged "12 volt" battery having an actual voltage of 13.8v, 6 cells @ 2.3v each = 13.8v. (Assuming the cells are in series)

Therefore your 12v battery has 6 cells and your 36 v battery has 18 cells. Actual fully charged voltage of the two batteries in series is 55.2 volts

If they are lead acid batteries then the rated voltage divided by 2. 2 volts per cell.

Let me wrap my head around this. You have (1) 36V battery, then you added (1) 12V battery to get to the 48V required for your electric motor. And Charging these with a 48 V charger. Before I can answer this. I need to know the Ah of both batteries, also need to know the charge rate and Amps of the charger you are using. Also what is the Ah, CCA of both batteries? I have been involved with Elco Electric boats for quite a while. Elco has been in the electric boat business since 1893. I work with 24, 36, 48, 72, 144V DC Drive Systems and we are recently working on 36, 48, 144V 3 Phase AC motor drive systems. 2HP through 28HP motors, experimenting up to 75HP. Charging is a complex issue with AGM batteries and their longevity. If taken care of correctly can service you for 12-15 years. You have not given enough info for me to make a decided decision on. Most of the batteries I use are 4D and cost $353.00 Ea. Weigh 153Lbs each. Put 36 of these in your system and you want 15 years out of them. So you must balance your chargers correctly.

Well as in my post both are 12ah. I'm at work and will see how many amps charger has when I get home. On the battery web site it doesn't give cca. This is the 36volt 12ah battery link. http://www.monsterscooterparts.com/36vomibai.html . The other battery is 12volt 12ah both are agm. This is the info given for the 12volt. UB12120 F2 D5775 12v 12ah New Sla Agm battery. Both batteries are meant for deep discharging for use in electric vehicles. The 12volt came from www.batterygeeks.com.

If each battery has an equal charge (% of full charge) and they are connected in series you will have no problems if they are at nearly the same age level.

The problems come in when you place batteries in series that are at different charge levels (the one with the lower charge stops getting charged when the more fully charged one reaches its full charge level).

It is common in heavy equipment and trucks to use multiple batteries in series to achieve higher voltages with greater amperages than obtainable with larger batteries (more cells and larger cells). The smaller ones are cheaper to manufacture and to handle. Also if one goes bad you don't have to replace the whole large battery, only part of the battery system.

This is also why battery back-up systems are made with numerous batteries set in multiple parallel/series systems.

Good Luck Old Salt

Provided both batteries were fully charged (or at the same state of charge - fully charged is easiest) when they were connected together it should be OK

They were both brand new and fully charged.

Then you should have no problems

Someone already gave some correct infos, but most of the infos here are incorrect or incomplete or are missing and explanation as to "why"?.

It does not matter what voltage you need 24, 36 or 48 volts), but when using multiple batteries, the batteries need to be from the same batch, from the same manufacturer, of the same type, bought on the same day for the best life/efficiency.

If you are not fiollowing this exactly, then the weakest cell in the weakest battery will fail first if charging to 100% full.

The only way round this is to only charge to around 70% or less. That way the batteries will have a very "full" life!!

If you didn't buy Leisure type batteries, then you need to charge them quickly once they fall below 12.6 volts per nominal 12 volt battery, otherwise sulfation will start.

Leisure batteries handle deep discharge far better but cost more and if you need sudden large amounts of amps, may need to be bigger in capacity to cope.

Chargers need to be matched to the battery(s) and NEVER gas the batteries, EVER....

Read the Battery manufacturer's recommendations fully through before starting....

Well thank-you for that info, thought I was all set now I'm not so sure anymore. You say never ever gas a battery, what is that? Second The battery charger is for charging batteries for an electric bike, 48volts which usually consist of 4 -12 volt batteries in a series.The charger says on the back, output DC 59volts 2.5 amps. I thought a 36volt battery had 18 cells wired in a series and a 12volt had 6 cells wired in a series encased in a sealed enclosure therefore if I connected the 36 volt to the 12volt it would be 24 cells all in a series. I guess this isn't how it works? The batteries were both made for deep discharge application (for electric vehicles) . So your saying if I charge them to 100% they will die real soon? Both the 36volt and the 12 volt will die prematurely and does that mean like in half the time or quarter? Could I charge the 12 volt with a 12volt charger and the 36 volt with a 36volt charger? And then put them back together? There wired with clips . Or am I just out the cost of the 36volt battery or should I just use as is an hope they last the summer. Usually the batteries are good for about 300 cycles depending how far you drain them each time. The less there drained the more cycles you should get out of the pack.

What I said was, if you charge 100% or to about 14.4 volts, the weakest cell will die first. I said cell not battery, though the battery with the weakest cell will be seriously affected.

If the batteries are not fully identical, you are always living dangerously, which is why I suggest to only charge to 70% capacity.....

How can I help further?

Thanks I am not battery savy that's why all the questions. The other thing I asked is what you meant by gasing so I make sure I don't. And when 1 cell dies I'll know it because the speed and distance I can go on the bike will be diminished? Also I asked if it would be better to charge each battery separate with there own charger?

Thanks for taking the time to answer these questions.

Gassing occurs when for example a 12 volt battery exceeds about 13.5 volts (that was from memory!), you will see bubbles in the acid. If the battery is not a sealed version, Oxygen and Hydrogen are given off as the water of the acid is driven off, if a spark happens you can get a bad explosion that will rip the battery apart.

Many have lost their sight through such explosions (inspecting a battery with a cigarette in the mouth or hand was common at one time!!)

Look here:-

http://en.wikipedia.org/wiki/Lead-acid_battery#Risk_of_explosion

and this can happen:-

Most cars charge to around 14.4 to 14.7 volts, but the car is outside and the gassing is not a problem outside.

Charging a bank of cells, no matter what the battery chemistry is, "full" always damages the weakest cell first, which is the reason why many car batteries do not live beyond 5 years of so. Many considerably less.....

This is considered normal & OK for cars......but a reasonable quality LA Battery, with careful usage, can probably live anything up to around 100 years or so. Some submarine batteries still in use are 50 years old or more and have been in many subs.....Battery backup for telephone exchanges can also live to a great age......

I found this:-

Battery LifeBattery manufacturers define the end-of-life of a battery when it can no longer hold a proper charge (for example, a cell has shorted) or when the available battery capacity is 80% or less than what the battery was rated for. The life of Lead Acid batteries is usually limited by several factors:

• Cycle Life is a measure of how many charge and discharge cycles a battery can take before its lead-plate grids/plates are expected to collapse and short out. The greater the average depth-of-discharge, the shorter the cycle life.
• Age also affects batteries as the chemistry inside them attacks the lead plates. The healthier the "living conditions" of the batteries, the longer they will serve you. Lead-Acid batteries like to be kept at a full charge in a cool place. Only buy recently manufactured batteries, so learn to decipher the date code stamped on every battery... (inquire w/manufacturer). The longer the battery has sat in a store, the less time it will serve you! Since lead-acid batteries will not freeze if fully charged, you can store them in the cold during winter to maximize their life.
• Construction has a big role in battery life too, some designs are better at preserving batteries than others and the suitability of a design for a given application plays a role also. For example, flooded lead-acid cells will typically fare worse than their VRLA cousins in operations that involve a lot of jerky motion - the immobilized plates in VRLA cells will be stressed less than suspended plates in cheap flooded cells.
• Plate Thickness helps - the thicker the plates, the more abuse, charge and discharge cycles they can take. Thicker plates will also survive any equalization treatments for sulphation better. The heavier the battery for a given group size, the thicker the plates are, so you can use weight as one guide to buying lead-acid batteries.
• Sulphation is a constant threat to batteries that are not fully re-charged. A layer of lead sulphate can form in these cells and inhibit the electro-chemical reaction that allows you to charge/discharge batteries. Many batteries can be saved from the recycling heap if they are Equalized

In closing, the design life of a battery depends in part on its construction, its type, the thickness of the plates, its charging profiles, etc. All these factors come together to determine just how long your battery may ultimately serve you.

Here:-

http://www.vonwentzel.net/Battery/00.Glossary/

There is plenty of good information on the web to read and inwardly digest......these were just a few examples for you.

If I can help further, please just ask.

By the way, never charge batteries in an un- or poorly- ventilated place, the gas can build up and ignite with a tiny (unnoticeable) spark of static discharge.....

Re: I thought a 36volt battery had 18 cells wired in a series and a 12volt had 6 cells wired in a series encased in a sealed enclosure therefore if I connected the 36 volt to the 12volt it would be 24 cells all in a series. I guess this isn't how it works?

Yes, that is how it works!

But, in answer to your question in the your last post, I think you would be somewhat better off charging each battery with a properly rated charger (i.e., 12 volt for the 12 volt batter, 36 volt for the 36 volt battery. Then, yes, you can put them in series again (to get 48 volts) for use.

Especially if the alternative is to be out the cost of the 36 volt battery. I think you will get a reasonably long life with this approach. (You might be fine with the 48 volt charger, but I'd be a little more confident with the 36 and 12 volt chargers.)

If your batteries are rated at the same volts/cell, the same Amp-hr/battery-cell and you start them at the same charge level at the initial use, then neither the individual batteries or the cells or for that matter if you are using them in series--> neither the batteries, the cells or the charger can't tell the difference between what battery the cell is located in and therefore will electrically act as though they were in the same battery body.

One cell goes bad will be at random, not selectively as some might suggest. If you charge them in series and discharge them in series they will act as one unit.

What I suggest you do is fully charge them individually, since new batteries are not necessarily fully charged, place them on your scooter in series, use them in series, charge them in series and most of all ENJOY THEM IN SERIES AS YOU RIDE YOUR SCOOTER! Yes, I am jealous that scooters are no longer my thing, too many years and too many pounds! I need the extra mass of a Harley.

If the 48volt charger is truly a 48v battery charger it will produce the 55.2volts necessary to charge the battery unit. Enjoy yourself, just remember to unplug the charger before going for a ride!

A word of caution though: You do not know the qualifications of the submitters to this forum. Some may not know much about the subject but post as if they are the authority on the subject, some may know enough to be considered experts on the subject but aren't extremely good at communicating the subject matter, some ask more questions than they really need to to give you the necessary answer and only confuse you and lastly some should never be permitted on this forum. I am not passing judgement on any particular poster, only trying to spread some caution. Myself, I try to keep my answers as simple and understandable as possible. Sometimes I am successful at this and sometimes I'm not.

Good luck, Old Salt

Thanks I think I got all the info I need now and I did realize I was going to get allot of different answers so I'll just take yours cause it's the best for me LOL. thank you and everybody for there input . I will just use the batteries like they are and see how long they last. If they don't last next time I'll buy 4- 12 volt batteries or spring for a LifeP04 battery from LI Ping . Probably about 750.00 bucks though. Why don't they make a 48 volt battery so I don't have to combine 4 batteries to get 1. Maybe the cost ? I don't know. The 36volt was only 89.00.

Just a word of warning about LiPos, they are a brilliant technology, but need expensive and VERY proper charging and care.........they are liable to explode when wrongly charged or put on the wrong charger.....as many laptop owners have discovered over the years!!!

Hi ...

I been watching this thread with very much interest. I also just ordered 4 x 12v 12ah

sealed batteries for my 48v ebike. They are all the same brand and i'll make sure that all 4 is fully charged when i wire them up in series. What is the best charger i should use? 48v 2.5 amp charger? or ?

The batteries i'm getting is the Yuasa(American brand) or something like that. i'm told they are the best money can buy..is this true? or can you think of a better brand?

if i wire these 4 12v 12ah battery in series, will that make 48v 12ah? does the 12ah stay the same? or do i times that by 4? should i then be buying 12v 20ah? for more power and run time?

thanks.

kersley

Make sure each battery is individually fully charged (with a 12v charger) before you put them in series.

48v 2.5a charger is ok. Anything larger will not charge the batteries much faster due to saturation.

Yuasa are good.

Wiring the batteries (12v 12ah) in series will make your battery bundle equivalent to a 48v 12ah battery. To increase the amp-hr of this bundle you need to increase the amp-hr of the individual batteries within the bundle. If you do this with batteries of different amp-hr ratings you are limited by the lowest amp-hr battery.

Remember, your 12v batteries with 6 cells each are equivalent to a 48v battery with 24 cells with the cells in 4 different containers. What is internally wired in a 48v battery are now externally wired with the 4ea 12v batteries.

Good Luck, Old Salt

Hi: figured I would update my findings after wiring the 36 volt and 12 volt batteries together. The battery pack is not doing well as of right now anyway. It worked well up until just recently, the range has decreased quite abit and the power is noticeably lower as well. Now it's a struggle to make the 8 mile trec to work. Time to replace battery pack. I think I will go with 4 12volt 12ah batteries this time. I think the life of the pack will be much better this way . Then again I may go with the 48 volt lifePo4 ping battery. I have a ping 36 volt 20ah battery and am very happy with it on my 36 volt bike set up. I can go 40 miles on a charge and no power loss. It's suppose to last 5 years so the 570.00 spent including shipping is a good deal. The weight is about 14 lbs compared to about 32 lbs. for the SLA battery pack. All I need is some more money! ):

Thanking you both for the advise...I just seen on ebay a 12v 33ah battery SLA..

having 4 of these at the back of my bike.. would really pack a punch, however if the battery drained and i had to pedal home. It would be like pedaling a motorbike.

If only these hub motors were running on 12v 1000 watts. wow, if only...

I know what I would do in such a case, I would program a simple PIC to check the voltages of EACH BATTERY SEPARATELY, say once a minute while using the vehicle, and display it on an LCD display. It would also warn me when a specific level of discharge on any single battery was reached.

You may want to be able to switch out any discharged battery (to stop damage) and allow you to run further on a reduced voltage......

I personally would make sure that no single battery ever got drained and therefore reversed voltage across it as this severely damages any battery.

Leaving any battery discharged for more than a few hours will also damage it.....slightly, but it all adds up to a shortened battery life.

Make sure that you only buy batteries that will only be say 50% depleted by a days usage....that way you can charge them up each night and none will get reversed......their life will be long and happy.....