not the same capacity (AH) but the same chemistry is better.

Ok, thanks.

 

Aussie Paul. 

Baz421 wrote:

---

Paul

I disagree with previous posts in that the batteries should be the same, ie identical to each other.

Internal resistance and charging/discharging can result in serious imbalance in batteries in parallel.

Also it depends how they are wired. I found this out the hard way years ago when I kept killing one of the 12V boat house batteries (in a bank of 3).

Suggest you read the attached info from the UK it explains it in simple terms so suits me.

http://www.smartgauge.co.uk/batt_con.html

---

 Ok Baz, great link. Thanks. As the the old Castrol advert said oils ain't oils. Battery circuits ain't battery circuits!!!! I love simple....

 

Aussie Paul. 

-- Edited by aussie_paul on Friday 11th of April 2014 10:40:35 PM

Baz421 wrote:

---

Paul

I disagree with previous posts in that the batteries should be the same, ie identical to each other.

Internal resistance and charging/discharging can result in serious imbalance in batteries in parallel.

Also it depends how they are wired. I found this out the hard way years ago when I kept killing one of the 12V boat house batteries (in a bank of 3).

Suggest you read the attached info from the UK it explains it in simple terms so suits me.

http://www.smartgauge.co.uk/batt_con.html

---

 

 

HI Baz 

That link is primarily aimed at high charge & discharge rates & shows  the ideal set ups for any parallelled battery set up

Fig2 arrangement& is not complicated & suits the great majority of purposes

What is important is to have the same length & size cables for ALL those battery interconnections.

Regarding replacing with EXACTLY the same type, size & age batterries & some claim even brand ,well if one likes throwing their money away by all means do, that but in practise that is rarely necessary.

The biggest problem with not replacing al the batterries is that the older ones may delevop a leakage or short that discharges the newer one

IF that is not detected [by the bank quickly discharging] all the batteries in that bank will have a short life

But that can happen at any time, even with new batterries

With the normal charge & discharge rates used by the great majority of RVers, slightly lower or higher capacity batteries can be parallelled with very little problems

Of course that is within reason, one should not parallell say a 20A hr with a 100Ahr

Although in pratical use that can occur by natural aging.

 

CHemistry  can have a bit mor eefect, butthat is more associated with the charging settings

Mainly taking care to not overcharge  or possibly not  equalise charge sometypesof lead acid batterries

 

If one is realy keen to get longest life possible, the rules are simple

DO not over discharge fot the types used if mixed consider the type that can be the least discharged as the limit ]

Use either a volt meter or a battery monitor to ensure they are not accidently overdischarged

Check the battery makers specs for charging requirements,set the charger to the requirement of the battery which has the lowest max recommended charge voltage

Check if there are any equalising requirements for all the batterries, but if any should not be equalised, make sure they are kept within THEIR recommended voltage limits

IF flooded wet cell make a point of checking the electrolyte level regularly & topping up only with distilled or demineralised water

IF that is required frequently ,there is a charging problem,  could be  due to overcharging,  charging to fast ,.float charge level set too high .

Then one final point for long life do not excedd the make'rs recommended CHARGE rate [Amps]

DO NOT FAST charge unless the make gives some guidance

 

 

 

HI Baz

How can one come up to charge quicker than the other?

They are both/ all being  charged by the same charger

Each will have the same voltage at its terminals

Each will be at the same % SOCs under normal RV use[ NOTE, percent SOC  not Ahrs capacity] 

The 20Ahr  cannot be fully charged & say the  100Ahr only have 20Ahrs of capacity

 THe problem is more pronounced [of different SOCs] when the batterries are some distance apart & with light cables &  unbalanced cable resistance between the critical interconnections

Voltage drop in the cables then leads to a significant diference in charge & discharge percentage SOC

 

As I have said with high loads &/or very fast charging,with poorly balanced interconnections & batterries with widely varying capacities  can cause some problems.But for most RV use there is no problems

In fact  even IF you start with the same Ahr NEW batterries, it is very unlikely they will have exactly the same CAPACITY. but the SOC will even out

Marked Capacity & 100% SOC are not the same thing

OF more importance ensuring equal % charging/discharging is making sure the Actual Battery connections are kept clean & tight

That is were the usual problems arise  & can go undetected until to late!! when one battery ,[the one with good connections] has realy copped it

PeterQ 

 

.

-- Edited by oldtrack123 on Saturday 12th of April 2014 09:56:55 PM

-- Edited by oldtrack123 on Saturday 12th of April 2014 10:01:00 PM

I can only add this to this thread, when I was in the RAAF as an avionics tech we were told that cells and batteries in paralell had to be the same capacity. However we only dealt with lead acid and nicads these new fangled batteries are beyond me, the ones I have in my van can only be discharged to 50% rated capacity, so I ask why call them 110AH? why not 55AH? I dont get it......