# Another battery question.

Discussion in 'The Beginner' started by irnbru, May 11, 2014.

1. ### irnbruFunsterLife Member

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After just purchasing 2 new leisure batteries I am trying to get a better understanding of how they operate in the hope they will last a few years. So far I have learned that 2 batteries in parallel shows up like 1 big battery so can someone explain

1.How the 2 batteries discharge. Do they do so at the same rate or does one run to half empty 1st?
2. Does the system stop producing battery power when the batteries reach maximum discharge limit or is it up to me to monitor the level on 1 or 2 of the batteries each time we use them? If I have to monitor at what level on the meter would be the lowest to use, sorry if im confusing you.

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2. ### pappajohnFunsterLife Member

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as both batteries appear as a single large battery they discharge as one battery.

The batteries will discharge to a dead state eventually (0v) and will not recover when charged.

Its up to you to monitor the discharge and act accordingly...ie: recharge when at a max of 50% discharged.
50% equates to approximately 12.2v

3. ### irnbruFunsterLife Member

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Thanks for the reply but this is confusing me more now. When the banner batteries were put in two days ago the meter reading was 12 point something so after 50 percent they should still read 12. Something?

4. ### mazFunster

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That 'point something' is the important bit. 12.7v = ~fully charged, 12.3v = ~50% charged.

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5. ### pappajohnFunsterLife Member

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no....fully charged, but not on charge, they will show 12.6v to 12.7v.

As the batteries are used the voltage drops to a point they cannot provide enough volts to power the appliance, whatever that may be.

Akin to filling water glasses from a jug...each glass takes a little more from the jug until eventually the jug is empty and you drank the water in the glasses.

A 12v light bulb will still work at 11v but will be extremely dim compered to running at 12v or more

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6. ### irnbruFunsterLife Member

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Aaah think im getting it now. :thumb:

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7. ### UK PeteRead Only Funster

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Also batteries have a limited amount of charge disharge cycles, so not letting them run down to as low as 50% helps them last longer as i understand it
pete

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8. ### TootlesFunster

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There is a 'rule' that batteries coupled together either series, or series parallel, should be all of the same size and amp-age capacity.
Never found it matters personally, however............

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9. ### irnbruFunsterLife Member

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Wha can I get for point 4.?is it equal to so many amps?

10. ### pappajohnFunsterLife Member

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very loosely, yes.

110ah battery at full charge (12.6v/12.7v will have 110amps stored.

12.4v is around 25% discharged so capacity is around 77amps

12.2v is around 50% discharged so 55amps capacity....for our purpose technically flat.

Once a battery gets below 50% discharged it starts to oxidise the lead plates and this causes the charging process to work so much harder to recharge....over time it becomes impossible for the charge current to pass into the battery due to the amount of oxide on the plates.

If charged straight away, or as soon as practicable, from 50% the oxide is easily broken down and the battery accepts a charge.

11. ### irnbruFunsterLife Member

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So if i use 50 percent how many amps do i have to play with. Sorry but dont understand the last answer.

Ps I have 2 batteries together.

Last edited: May 11, 2014
12. ### pappajohnFunsterLife Member

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from fully charged you have 55amps to play with from a 110ah battery.

After using those 55amps (50% of fully charged battery) you need to recharge the battery or risk damaging it.

I know the battery holds 110amps but thats how it works unfortunately.

13. ### UK PeteRead Only Funster

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If you use 50% of your battery power you have taken it to its limit so you really dont have anything to play with if you want to keep the battery in good health, although technically you will half the amp power stated on the battery but as mentioned you will be doing the battery harm
pete

14. ### irnbruFunsterLife Member

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So whats the point in having 2 batteries linked together? Does that give me 110 or even 100 to play with?
Thanks for your patience while i continue to get my head around this.

15. ### TootlesFunster

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Supposedly, a 'leisure' battery can re-coup more of it's am-page capacity then a traction battery, (from total discharge), however, (unless things have changed since this happened to me), charging over ten amps can buckle the plates, causing the battery to be useless within a short time, (12 months with me).
This might be different now????????

16. ### pappajohnFunsterLife Member

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correct.....2 batteries joined pos terminal to pos terminal and neg to neg will give you 110amps to play with and will still be 12v.

I have 4 x 110ah so have 220amps to play with between charges

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17. ### mazFunster

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Try thinking of it as a balancing act - what you take out against what you put in - and aim to keep the battery voltage (off load) at around 12.7 or 12.6 v. Yes, you can let it drop lower than that on occasions but when it gets to 12.4v, that's when I'm rummaging in the locker for the generator.

18. ### peterc10Funster

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If you link two 110Ahr batteries together in parallel then you have 220Ah total. 50% of that means that you have 110Ahr to use up before you recharge, rather than 55Ahr if you only had one battery. Ahr is short of amp hours, i.e. amps used multiplied by the number of hours you are using it.

Amps x Volts = Watts. So for every watt of power you use in a 12v system you use one twelfth of an amp per hour of use. So check the wattage of each appliances and bulb, divide it by 12 and then multiply it by the hours you will use it. Do that for each appliance and then add them all up to give you the Ahrs you are using.

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19. ### irnbruFunsterLife Member

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I think I must be getting short changed here. Our batteries were fully charged yesterday morning, now reading 12.3
We have only had tv on about 4 hrs. Been charging mobiles and tablets, not used much light either. Heating been running approx 3 hrs. For 2 batteries I was expecting much more.

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