Problem Charging Aux Batteries with Smart Charger

I have some questions based on problems similar to those discussed in this thread

my dual battery set set up is the standard
OEM starter battery ( 90 AH )
Optima yellow top ( 55AH)
Traxide SC 80
Anderson plug at rear connected to Optima yellow top

I have been trying to fully charge my two batteries with a 5 amp 8 phase charger
I left it plugged in to the Anderson plug ( and optima 55 ah battery) most of yesterday and all last night but cannot get past STEP 4 (absorption ) on the charger

This morning I clipped the charger directly to the starter battery and after 4 hours it still has not progressed past the absorption (phase 4)

The SC80 has a solid green light and the voltage on both batteries with the charger on is 14.5
volts ....so the charge is flowing into the starter battery and across to the optima second battery

I have read above that the time to charge my batteries should be
90 AH + 55 AH =145 AH / 5 amps = 29 hours .......is this correct or is my charger too
small for the job ?

Do I need a bigger charger or am I just being impatient and eventually
my charger will eventually get to the float phase ( step 7)

The charger I'm using says (" battery capacity 10-120 ah ....maintainance charge to 200 ah")
given my batteries are 90 ah and 55 ah and the charge flows from one to the other ( either way ) should I be looking at a stronger charger........or again is it just a matter of time for the both batteries to get to the float ( step 7) and pulse ( step 8)

I’ve had this before. It’s more about the vehicle waking up and pulling that little bit off the top...

I wouldn’t panic at all.

If it makes you feel all good, I purchased a 25a ctek and that can get on top of them but I’ve found no benefit in doing so...

Hi Landoman, as Tombie posted, don’t panic.


Also, forget you math, the charger actually does not work that way.


While the batteries are low, they will draw the full 5 amps from your charger.


But as the batteries get close to a fully charged state, they will draw less current and this may cause your charger to take a much longer time before it decides to go into the float stage.


This is not a problem, just leave your charger on and see how long it takes to go into the float charge.


BTW, if your batteries are in need of a good charge, in other words, if they were in a poor condition, this will cause the charge to stay in the ABSORPTION stage for a long time, while the batteries regain some/all of their lost capacity.


PS a small charger is much better for your batteries than a big one.

Thanks Tombie and Drivesafe ...........
..Yes Druvesafe I suspect the batteries were in pretty poor state of charge as I had run the optima down to very low on a few occasions and only ever charged both batteries via the alternator while driving ......this is the first time I have used a charger to try to get them fully to top charge ........so you reckon just keep my 5 amp charger on then and eventually they will get to float stage ?

Quote:

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Originally Posted by landoman

Thanks Tombie and Drivesafe ...........
..Yes Druvesafe I suspect the batteries were in pretty poor state of charge as I had run the optima down to very low on a few occasions and only ever charged both batteries via the alternator while driving ......this is the first time I have used a charger to try to get them fully to top charge ........so you reckon just keep my 5 amp charger on then and eventually they will get to float stage ?

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I charge my batteries often,with the same charger as yours,as my vehicle sometimes sits around, we have company cars.

I also have the Traxide SC80 D4 Traxide kit.

I find the best way is to charge the batteries separately,and never let them get too low.Mine will often be on float in a few hours,or overnight at the longest.I have never seen it not go to float,as yours is doing.

One of your batteries may be faulty,isolating and charging them separately may be the go,to determine which one is the problem battery.

The easiest way to isolate the batteries is put a switch in the earth wire,running from the SC80.

As a battery becomes fully charged, the current it takes from the charger drops. Chargers typically go into float mode by sensing this drop in current This is how the charger determines the correct time to go into float mode. However, in your case you have two batteries each drawing a little current PLUS the current taken by the Traxide unit. Thus the charger never sees a low enough current draw to go into float mode.
As Scary said, isolate the Traxide by removing the earth lead - this will stop the Traxide drawing current and then you should charge each battery separately. There is a risk of over-charging and damaging the batteries if the charger never goes into float mode.

The other thing i forgot to say,is lock the vehicle as well if you can,as it will draw less power from the batteries,it goes to sleep.
Leaving it unlocked it is not asleep,so draws more current from the battery.

This is difficult to do because if the bonnet is open you will have to loop out the bonnet switch to lock the vehicle.

Hi again Landoman, if you still have the charger connected and on, try measuring the voltage at both batteries.

This can give you an idea if the batteries are near fully charged or if the voltage is down a bit because something is continually pulling current.

Quote:

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Originally Posted by drivesafe

Hi again Landoman, if you still have the charger connected and on, try measuring the voltage at both batteries.

This can give you an idea if the batteries are near fully charged or if the voltage is down a bit because something is continually pulling current.

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Ok I left the charger on all of yesterday and all of last night .......the charger is still on
step 4 absorption phase ...it has not gone to float phase

this charger has a recondition mode and that is what I have the charger set on
....it has an extra recondition step 6 before it goes to step 7 float

the voltage on both batteries ( with the charger on and connected ) is 14.5
i have removed the charger now and will let the batterie sit and rest and see what the voltage is after a few hours .

as I am doing this on a defender 110 and the two batteries and SC80 are in that very tight battery box under the passenger seat it's very hard to get at the earth wire on the SC80 to disconnect it
is there another easier way to disconnect the SC80 .....say taking the leads off the terminals ?
If so which leads if not all of them

I could then then try to charge each battery seperatly as suggested and see if I can get either of them to recondition stage 6 or float stage 7 .

appreciate all the advice .....both batteries are less than 2 years old so I'm hopeful they are both still good .