Charging Batteries In Parallel

[B@ssCrzy]

 

I have a Dual Pro Charger Sportsmans Series, 2 bank battery charger, 10 amps per bank, for a 12v system.  I am looking at buying two new deep cycle batteries to run in parallel with each other.  So what I am wondering is if my charger can charge these batteries with one of my banks or do I need to buy a single bank charger to put on my cranking battery and dedicate the Dual Pro Charger to my deep cycles?  Any thoughts would be appreciated.  Thanks guys!!

[Jig Man]

You can do it like you think.  The charging time will be a lot longer with one bank on 2 batteries.  Either one of your ideas will work depending on how long you have to let them charge and if or not you want to invest in a charger for the cranker.

[jhoffman]

Why are you putting them in parallel? 12 volt TM and you want more time?

 

Parallel = same voltage, double capacity.

 

You should be fine to charge the parallel setup and the cranking battery. However, keep in mind its likely going to take twice as long to charge the parallel setup as the cranking battery.

[00 mod]

Also, you want to make sure both batteries are of the same age when in parallel.

 

Jeff

[Fishes in trees]

I have a similar set up I run one bank to each of the trolling motor batteries.  The cranking battery seems to take care of itself.  When my big motor is running, it charges up the cranking battery.

 I haven't had any power issues.  I swap out batteries every other year. 

[PotomacBassin]

When you do this, do the CCA ratings need to be the same?  I figured they don't. 

[jhoffman]

I wouldnt think, its still 12 volts no matter how big the size. CCA doesnt matter on trolling batteries

[PotomacBassin]

I wouldnt think, its still 12 volts no matter how big the size. CCA doesnt matter on trolling batteries

Well how do you tell the capacity of the battery then?  I guess my question is does it matter if the trolling batteries are the same capacity?

[jhoffman]

Well how do you tell the capacity of the battery then?  I guess my question is does it matter if the trolling batteries are the same capacity?

 

Amp hour rating or reserve mins listed on the battery.

 

Lets look at a group 29 size diehard marine battery...

 

Specs:

   

Power Ratings: Amp Hours at 20 Hour Rate: 115

                         Cold Cranking Amps (CCA at 0 deg.F): 675

                         Reserve Capacity (RC): 200 min.

                        

 

 

 

 

If I am reading this right this battery will deliver 115amps for 20 hours

[PotomacBassin]

Ok,  to run in parallel, does it matter if they are the same capacity.

[PotomacBassin]

Amp hour rating or reserve mins listed on the battery.

 

Lets look at a group 29 size diehard marine battery...

 

Specs:

   

Power Ratings: Amp Hours at 20 Hour Rate: 115

                         Cold Cranking Amps (CCA at 0 deg.F): 675

                         Reserve Capacity (RC): 200 min.

                        

 

 

 

 

If I am reading this right this battery will deliver 115amps for 20 hours

I don't think 115 amp rate for 20 hours is possible on one battery.  That's another subject though.  I saw a Bill dance show where he gave a generic calculation for how long the trolling motor battery will last.  It wasn't exact but was a decent guestimation.  I forget what it was.

[PotomacBassin]

Did some research and I think an average battery is about 100 amp hours.  I have a a Minn Kota 55 lb thrust motor and it draws approximately 50 amps at full and constant speed.  At full speed, the battery will last approximately 2 hours simply by dividing 100 by 50.  I can't find the amp hours on my battery though.  I guess hybrid batteries don't alway list the amp hours.

[jhoffman]

I typed that wrong... 115 amp hours at 20amps

[PotomacBassin]

Amp hour rating or reserve mins listed on the battery.

 

Lets look at a group 29 size diehard marine battery...

 

Specs:

   

Power Ratings: Amp Hours at 20 Hour Rate: 115

                         Cold Cranking Amps (CCA at 0 deg.F): 675

                         Reserve Capacity (RC): 200 min.

                        

 

 

 

 

If I am reading this right this battery will deliver 115amps for 20 hours

Using your example, you can use the reserve capacity as a approximate for how long your battery will last.  200 min reserve capacity is the minutes the battery will last at 25 amp load.  So at 25 amp load, you battery will last 3.3 hours (200 hour/60 minutes per hour).  My motor at full speed at 50 amps would last about half that.

[BKeith]

Lets see if I can explain things a little better.

First a 115 Amp hour using the 20 hour rating basically a useless number. They are only using a very small, five to six amp load when testing this.

The reserve capacity is a much more useful number because it is usually based on how long a like new, fully charged battery will run a 25 amp load. However some companies use a smaller load like 20 or 22 amps to make their numbers look better.

The reason I say the 20 hour rating is useless unless you are only running a five amp load, as you increase the load on a battery, it's capacity to deliver current decreases. That's why you can't use the math saying a 100 amp hour battery will run 50 amp for two hours. If you put a 50 amp load on a 100 Ah battery, it will be much closer to 65 Ah battery, so instead of two hours run time, you get about 1 1/4 hours run time. That's why it's always better to run two batteries in parallel than running one until its quits and then connect to the second. The two in parallel half the load so drain is half, making runtime longer than running one at the time.

Also understand, not all batteries are made the same and some plate materials will handle heavy discharge loads better than others. That's why you can put a Trojan and a Wal Mart Maxxium side by side, with the same Ah capacity or Reserve minutes, with a heavy load and the Trojan will usually run a little longer under the same load.

[PotomacBassin]

Lets see if I can explain things a little better.

First a 115 Amp hour using the 20 hour rating basically a useless number. They are only using a very small, five to six amp load when testing this.

The reserve capacity is a much more useful number because it is usually based on how long a like new, fully charged battery will run a 25 amp load. However some companies use a smaller load like 20 or 22 amps to make their numbers look better.

The reason I say the 20 hour rating is useless unless you are only running a five amp load, as you increase the load on a battery, it's capacity to deliver current decreases. That's why you can't use the math saying a 100 amp hour battery will run 50 amp for two hours. If you put a 50 amp load on a 100 Ah battery, it will be much closer to 65 Ah battery, so instead of two hours run time, you get about 1 1/4 hours run time. That's why it's always better to run two batteries in parallel than running one until its quits and then connect to the second. The two in parallel half the load so drain is half, making runtime longer than running one at the time.

Also understand, not all batteries are made the same and some plate materials will handle heavy discharge loads better than others. That's why you can put a Trojan and a Wal Mart Maxxium side by side, with the same Ah capacity or Reserve minutes, with a heavy load and the Trojan will usually run a little longer under the same load.

Right, we're not trying to be exact (as we all know batteries are an inexact science).  But the calculations using the Ah or the Reserve capacity can give you a guestimate.  Thanks for your input.  

[Nitrofreak]

Well how do you tell the capacity of the battery then?  I guess my question is does it matter if the trolling batteries are the same capacity?

 

Roughly,  I think the best answer here would be to have them as close as possible, one concern I would have if they did differ too much is that depending on the users type of charger,  the overcharge protector may not be of use and could result in damaging one if not both of the batteries.

[PotomacBassin]

Ok so I just bought a battery to hook up in parallel. The guys at bass pro were telling me I can't charge both trolling batteries on one bank. I'm skeptical of their opinion. Should I hook the one bank up to both batteries or just have the charger on the positive and negative of one battery? I don't want to have to disconnect the one battery every time.

[Nitrofreak]

The best way is to just hook it,  one charger to one battery, if there is too big of a descrepency between the two the bank charger may end up damaging the battery,  it's not that it can't be done that way,  it's just much safer to have it on one battery.

[The Rooster]

From what I know, batteries need to be nearly exactly the same to parallel them. If not, the weaker one will drag the stronger one down to its level.

[Way2slow]

I could post the facts of does and don'ts, but from reading the other post, it seems anything other than what other certain people think would cause conflict, so I wouldn't waste my time