Batteries wired parallel ???

Submitted: Thursday, Apr 30, 2009 at 23:50
ThreadID: 68399 Views:3205 Replies:5 FollowUps:3
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Right, i think this is a pretty easy question for the gurus out there. Am i right in thinking that if i wired 2 12v 18 a/hr batteries together in parallel i would still get 12v and 36amp/hr.

Reason being is i have one battery already (thinking of buying another instead of Thumper or waeco power pack) and just want a back up device to run my Waeco CF35 ACverb for a few hours. Will only be used as a fridge set at around 2-3 degrees c, and it has the cover and will be in back of car in good shade. Will only ever be used at night actually for around 8-10 hours and it wont be getting opened at all during these hours, and would cooled down to its temeprature. Im guessing the ambient temps to be anywhere from 5c - 20c, so not hot at all.

Does this sound alright, i was thinking if it used a max of 2 amp/hours for around 10 hours = 20 amp/hrs, which leaves me at least 1/3 of my battery power to save batteries.

Only thing is charging the batteries, i currently have a SLA 1 amp battery charger that i charge my current battery with. It does a good job. But if i have it wired in parallel can i charge both at the same time through same charger. i know it will take longer, but is it safe or possible. Just looking for a cheap and easy way to get me by for the time being until i can get my dual battery system. Could be a while away so i really want something to fill the gap thats not overpriced like the Thumpers and stuff.

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Reply By: trainslux - Friday, May 01, 2009 at 00:12

Friday, May 01, 2009 at 00:12
Short answer is yes.


with deep cycle batts, you dont want to pull them down past 50%, or you shorten the cycle life avaliable to you by a large amount.
so by putting 2 in parralell, your getting 1 18ah battery, with some cycle life if that makes sence.

yes you can charge them in parrallel.

Head off to a battery place, and get a price on a sla 50 75 or 100+ ah battery, and fit it inside a cheap battery box with the fittings you require.
much cheaper than the thumper, and better performing too.

Yes you can do what your suggesting, but with money, and time, there are better options available to you if you know what I mean ;)

AnswerID: 362531

Follow Up By: Sand Man (SA) - Friday, May 01, 2009 at 07:23

Friday, May 01, 2009 at 07:23
Better performing???

If the Ah rating is the same how can it be better performing?

The Thumper actually has a group of smaller Ah batteries inside the box, connected in parallel to give the total Ah capacity of the unit.

I use both a Thumper (75Ah+) and an auxiliary Deep Cycle battery under the bonnet and I'm buggered if I can state categorically that the auxiliary battery is better performing than the Thumper.

As for cheap battery boxes, ever tried lifting one that has a 75Ah or 100Ah AGM battery inside?
The lid is secured with a strap and the handle is on the lid. Duh!



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FollowupID: 630254

Follow Up By: trainslux - Friday, May 01, 2009 at 18:15

Friday, May 01, 2009 at 18:15
If you take what I said in context, you will see that a larger amp hr battery will give better performance, or results, or better than what he currently has with 18ah.

And cheaper than a thumper setup.

is that more clear now??

I agree, both of the same ah would be the same, only the price could be different thumper vs battery and batt box setup.



FollowupID: 630353

Follow Up By: RV Powerstream P/L - Saturday, May 02, 2009 at 09:12

Saturday, May 02, 2009 at 09:12
Two x12V18AH batteries in parallel will stay 12V but increase in amp Hour capacity.
Two x12V 18AH batteries in series will give 24V and stay at 18AH

Dont forget that it is theoretical AH as you never get the full benefit of the stated capacity.
FollowupID: 630423

Reply By: Member - Tony S (WA) - Friday, May 01, 2009 at 00:22

Friday, May 01, 2009 at 00:22
Hi Kroozer,

Don't know alot about the Waeco however, one of my sons has a 40l? and has three 36amp. deep cycle batteries in parrallel and they last him [including a high performance floro at night 11watt for a couple of hous] roughly 31/2 days with out charging.
Talking to him he said that you will most probably be averaging nearer to 2.5 amps. My Engel starts off just over the 2.5amps and just before it shuts down is drawing 1.8/9 amps. You would have to put a meter in line to check the draw.
There must be someone out there who should be able to tell you more.

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AnswerID: 362532

Reply By: Michael ( Moss Vale NSW) - Friday, May 01, 2009 at 07:24

Friday, May 01, 2009 at 07:24
I have my patrol batteries wired in parallel because i have a thirsty fridge. I also wanted to avoid the extra wiring of a solenoid.. less parts, less to fail.. Michael

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AnswerID: 362539

Reply By: Axel [ the real one ] - Friday, May 01, 2009 at 09:54

Friday, May 01, 2009 at 09:54
Yeah ,that will all work ,BUT, really only a little but , your 1amp charger WILL do the job extremely slowwwwwly , take out amp hrs you have to put them back in , taking /using 20 for example your little charger will need to run for 20 hrs to replace it,, invest in a decent charger now ,something like a Ctek 7 or a 15 will last you through several upgrades of battery power qty.
AnswerID: 362556

Reply By: Inkbandit79 - Friday, May 01, 2009 at 20:31

Friday, May 01, 2009 at 20:31
Funny Kroozer, I wanted to do the same thing to my secondary battery for easter as i was running two fridges. I got told on here to wire them up in series, which i belive would turn the whole system two 24 volt, ie excavators loaders and trucks. Which would have probably r@@ted my system. if your in perth speak to john at Aust West auto elec he will send you down the right path
AnswerID: 362681

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