How long to recharge two batteries?

[Crispin]

I installed a Parrot car-kit on Saturday and on Sunday afternoon my LC would not turn over. Two batteries dead
After a bit of digging and chats with Tony about his parrot, we worked out the the loom I was given to connect the parrot to the LC's radio had the Ign and V+ swapped which had then drained my batteries (Two new 75AH Mr-T specials).

After a jump start I drove for around 30 minutes to the outlaws and back, This morning it turned over ok but not in it's usual excited fashion. I guessed the batteries were still not full.
Driving in to work (about an hour) and spending a day with Mr-T, no doubt with a few stops and starts, it was dead this afternoon. Starter turned once and died.

Another jump start and an hour worth of traffic, I got home and measured the batteries. They were 12.18V with the carputer and Parrot disconnected and the car pulling 20mA which I guess is ok.

Question would be, how long would it take my 120A (IIRC) alternator to charge the two batteries? If they were dead at the office, would an hour's drive suffice? If Mr-T did lots of starting, leaving the ignition on etc, would that have been enough to drain the hour's charge I put in during the drive in?

Once I got home, I stuck a charger on them and they were happly pulling 15A from it for 30 minutes (not checked since)

 

[Jon Wildsmith]

Did you test the batteries individually? It could be that one of them has gone bad and is draining the other?

 

[Crispin]

yup, one was 12.18, other was 12.2. The higher was tested with no load, the lower was with the car connected (doors close, key out etc)

Just checked the charger and it's now down to about 7-8A after about an hour on it.

 

[Jon Wildsmith]

Amps sounds a bit low for a pair of 75AH but if it's an intelligent charger then it may just be the stage it's at rather than the state of the batteries. I'd test them both disconnected, after allowing them to settle for a while or put the headlights and rear demisters on for a minute or two to remove surface charge. If one of them is still lower I think that indicates a problem. Charge will always go from the higher voltage battery into the lower voltage one and drain them both as if you had a load on. Might not be that but it's an easy thing to eliminate from your enquiries ...

 

[Crispin]

Does not look like that is a problem. (?)


NS OS
Open 12.29 12.30
car load (±400mA) 12.26 12.18
demister and highbeam 11.78 11.84


All these were with the opposite battery disconnected. After this quick test, I put the charger back on and it was back to 15A.
It is an "intellegent" charger so maybe it is going through the different stages. I'll leave it plugged in overnight and see in the morning.

After I connected the charger, the batteries were only showing 12.6V, I would have thought they would be pulled slightly higher.
Will see in the morning...

 

[Jon Wildsmith]

I wouldn't have thought that is the problem then. I had a pair of Elecsol's that wouldn't last as long as I expected because a cell went in one which kept draining the other so I always eliminate that first with dual batteries. An alternator isn't a very good charging device for recovering from a deep discharge so maybe a decent go on your intelligent charger and all will be back to normal.