# 12v battery banks and amp hours

So I'm new to the battery banks. One bank is (6) cells made of (2) 6v, 12 amp hour sealed lead batteries each. Wired parallel to make a 12v, 144 amp hour bank. Is that correct? Next I have a smaller bank, that is (2) 12v, 18 amp hour sealed lead batteries, paralled Making a 12v 36 amp hour, is that correct? If I'm on the right track I'm glad. So my last question is. If break my 2 battery bank down, so they are 18 amp hours. Will it hurt to tie them into the other bank where each cell is 24 amp hours? I know with big differences it is hard on the smaller amp hour batteries, but was hoping it wouldn't be the case here and I could get 180 amp hours if I'm correct. Thanks for any advice. Hope I'm on the right track....

• Please check and edit second and third sentences. They aren't making sense to me.
– user16324
Commented Nov 5, 2015 at 12:22
• Did that help the confusion? Commented Nov 5, 2015 at 12:42
• No. For a start, a battery is made of cells, not vice-versa. Then, if you wire 12 6V 12Ah batteries in parallel you would have a 6V 144Ah bank. 6 of those wouldn't give you a 12V 144Ah bank unless you kept 4 as spares. So I still don't understand.
– user16324
Commented Nov 5, 2015 at 12:47
• Now it confuses me even more. Better draw a diagram of what is in parallel en what is in series. For me a cell is the 2V part of a battery, so your using of the word confuses me. And the second sentence has 12 batteries of 6V 12AH each. If you put those in 6 parallel pairs of 2 you get a 12V, 72 AH combo, not 144 AH. Remember: parallel adds the AH, series adds the V. Commented Nov 5, 2015 at 12:50
• (12) 6v batteries to make, (6) 12v batteries. Commented Nov 5, 2015 at 12:50

I think something's gone wrong with your maths. If you connect two 6V 12Ah batteries in series, then you'll get a 12V 12Ah battery. Wire six 12V 12Ah batteries in parallel, and you'll only get a 12V 72Ah battery, not 12V 144Ah.

Maybe this will help. When you connect batteries in series the voltage adds the amp hours are equal to the lowest rated one. When you connect them in parallel the current (amp hours) adds the voltage remains the same. Never put parallel two batteries of different voltage ratings in parallel, or you will see smoke city.

Example: If you connect two 6 volt batteries in series you will get 12 volts, that can be paralleled with another 12 volt battery but you cannot parallel a 6 volt and a 12 volt battery.

Batteries are made up of cells (2.2 volt batteries). A 6 volt will have three of these in series and can have many parallel strings each string with three cells in series. A 12 volt battery is the same but has six cells in series.

If you charge them expect 80% efficiency on a good day. Simply stated to get 80 Amp Hours charge you need to add about 100 amp hours.

Hopefully this helps.

Gil