Thread: What Happens If I..?

You would have 80.

yep you should have 80 amp hours.

just remember in this configuration if one battery dies it will normally take the other battery with it.
I wouldn't be too worried about it but I just thought you should know

If you connect positive to positive and negative to negative you get 12volt and 80.
If you connect pos to neg you get 24volt and 40 still.

Mike

Paralleling the batteries to give 80AH will work, but be warned that this is considered bad practice. It will be OK provided the batteries are identical, but the problem is that even if they start out identical, they don't stay that way.

One battery will soon get a higher charging voltage for the same state of charge, and hence will never get its share of charge. So we end up with one battery being overcharged and the other undercharged. The overcharged one will probably fail, and take the other one with it.

Temporarily paralleling the batteries is unlikely to give any problems, but I would not do it long term.

John

What if I hooked up an 80 amp/hour (same type) and a 40 amp/hour? Am I being too ambitious here.
I have a C-Tek 12V DC to DC charger (25 amps) in my Camper Trailer (C/T), would it charge both 40 amp batteries evenly, it works off power cable from Disco main battery when ignition (key) on or 240 amp solar panels when camping, thanks for the other replies, Regards Frank.

Originally Posted by Tank

What if I hooked up an 80 amp/hour (same type) and a 40 amp/hour? Am I being too ambitious here.
I have a C-Tek 12V DC to DC charger (25 amps) in my Camper Trailer (C/T), would it charge both 40 amp batteries evenly, it works off power cable from Disco main battery when ignition (key) on or 240 amp solar panels when camping, thanks for the other replies, Regards Frank.

Same problem as I outlined above, except that it would be worse as the batteries are different to start with. To avoid problems you would have to use two separate DC to DC chargers, one for each battery. (assuming I understand clearly what you are proposing!)

John

oh yeah only connecting them parallel will give you 80 amp hours. forgot to mention that bit.

but it seems connecting batteries this way isn't the best.

How do battery banks in say house set ups work then? or are they in series?

I have my batteries for my fridge wired up in parallel and all has been fine. I would suspect the batteries would have a shorter life expectancy though wired this way. I do work them pretty hard though so that is to be expected.

Quote:Paralleling the batteries to give 80AH will work, but be warned that this is considered bad practice. It will be OK provided the batteries are identical, but the problem is that even if they start out identical, they don't stay that way.

One battery will soon get a higher charging voltage for the same state of charge, and hence will never get its share of charge. So we end up with one battery being overcharged and the other undercharged. The overcharged one will probably fail, and take the other one with it.

Temporarily paralleling the batteries is unlikely to give any problems, but I would not do it long term.

John


John, I don't understand why "paralleling" the identical 40 amp/hour batteries would cause problems, my current truck ACCO Inter 8 tonne T/top runs on 2 X 12V batteries, wired parallel for 12V and just about every truck I've had over the years has had multiple batteries to give 12V and I've never had a problem.
I was thinking of running 2 new Optima yellow Top, deep cycle 40 amp AGM batteries in my C/T giving me 12V and 80Amp/hr.
Is there any reason the C-Tek (20amp not 25 as stated in previous post) would not charge these 2 batteries evenly, Regards Frank.