Amp Hours on Joining Two 6v Batteries to Make 12v . . .

[Ocean Roads]

My trusty West catalog says that their 6V battery has an amp hour of 215 Ah.

Now, when you hook two 6V together to get 12V, does your Ah stay the same, double, or get cut in half?

Trying to build a nice house bank, but I need to know how many 6Vs I will need to get the desired amp hours for my bank.

[s/v 'Faith']

In series (as to make 12vdc from 2 6vdc batteries) the ah capacity stays the same as the rating.

2x 6v 215ah batteries = 12v at 215ah.

[Alecadi]

with 2 identical batteries
if you connect them in serie: you double the voltage but keep the same amperage
if you connect them in parallell: you keep the same voltage but double the amperage

[GordMay]

Series battery connections result in doubling voltage, whilst capacity remain the same.
Parallel battery connections result in voltage remaining the same, but capacity doubling.

Two 215AH 6V batteries in series will result in a 215AH 12V bank.
Four 215AH 6V batteries connected in series-parallel will result in a 430AH 12V bank.

[S/V Alchemy]

I have been "garage-feeding" two 12 VDC house batts and two 6 VDC in series via a couple of the fancier sort of trickle chargers (up to 6 amps, which is a fairly robust "trickle".)

I follow the usual method of laying on a day or so of charge at a high (14.2 VDC) voltage, and then throttling back for another day. After a "day of rest", they read 13.2 for the new (2010) 12 VDC and 13.1 for the six year old 6VDCs. My conclusion, having eventually killed, despite loving care, a few 12 VDCs in my time, is that the 6 VDCs are somewhat more durable. Admittedly, this idea was formed when I got the boat and series-wired 6 VDC Trojans were able to crank my diesel, despite being 18 years old (!), but others have also suggested that 6 VDC "golf carts" are the road to longevity in the battery department.

[btrayfors]

Yes, the 6V golf-cart or industrial batteries are likely to last longer than their 12V cousins because they have thicker plates and often more robust construction.

Note that the 13.1V you're measuring on the 6-year old batteries says NOTHING about their capacity or overall health. The ability to "take a charge" is not the same as the ability to store and delivery energy (capacity). Only a proper load test can tell you their true health.

Bill

[David M]

The confusion here is that volts times current (amps) equals power in watts. Although the amp-hours remain the same by doubling the voltage you have doubled the stored power. Or another way to look at it is you can now draw twice the current and have the same theoretical voltage drop in a given amount of time.

[S/V Alchemy]

Originally Posted by btrayfors

Yes, the 6V golf-cart or industrial batteries are likely to last longer than their 12V cousins because they have thicker plates and often more robust construction.

Note that the 13.1V you're measuring on the 6-year old batteries says NOTHING about their capacity or overall health. The ability to "take a charge" is not the same as the ability to store and delivery energy (capacity). Only a proper load test can tell you their true health.

Bill

Yes, I know that but thanks for the reminder. They have been babied and, being an "econo-cruiser", I know how to service and keep healthy wet-cell batteries.

These will probably be retired to the garage where I can test LEDs and play with my ICOM M-802 before it goes aboard the boat when the mast goes back in.