How to check Battery

Hi, I have a 120ah AGM fullriver battery & was wondering how I can check how much charge or AH is left in them. I just measured 12.9Volts with a multimeter..
Can you tell by this number & is it specific to each battery ?
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Reply By: Best Off Road - Friday, Jan 15, 2010 at 14:08

Friday, Jan 15, 2010 at 14:08
Try this site

Battery Information

Check out the "Battery Voltage" section. I'd also recommend reading the whole thing; quite interesting and informative.


AnswerID: 399566

Follow Up By: ss--ss - Friday, Jan 15, 2010 at 14:41

Friday, Jan 15, 2010 at 14:41
Thanks This link was very helpful
FollowupID: 668535

Reply By: kiwicol1 - Friday, Jan 15, 2010 at 14:46

Friday, Jan 15, 2010 at 14:46
best way to check a battery, fully charge it on charger let sit over nite, take to auto sparky and get him to load test it. Col
AnswerID: 399572

Reply By: outsider - Friday, Jan 15, 2010 at 15:06

Friday, Jan 15, 2010 at 15:06
I tested my 90 AH battery by drawing a continuous 3 amp load out of it with the inverter plugged in, got about 7 amps out of it (2.5 hrs) before the low voltage alarm on my inverter kicked in.

Guess I need a new one.......

Not sure how you're suppose to test them but this gave me a fair idea of the condition of the battery

AnswerID: 399577

Reply By: Roughasguts - Friday, Jan 15, 2010 at 18:31

Friday, Jan 15, 2010 at 18:31
I am no expert on batteries that's for sure but a good battery will have when fully charged 2.2 volts per cell, so that would be 13.2 volts for a good battery if left overnight with out charge.

I find when charging a good battery every cell will bubble evenly with the next one. But if your battery has had it's day! one or more cells can be buggered and will not bubble when on charge, so that leads to a drop of 2.2 volts per cell that does ot bubble when on charge.

Simple I know but it has worked for me.

AnswerID: 399609

Follow Up By: Member - Andrew (QLD) - Friday, Jan 15, 2010 at 18:48

Friday, Jan 15, 2010 at 18:48
Hey Rough,

An AGM's not going to bubble. LOL

FollowupID: 668571

Reply By: Hairs & Fysh (NSW) - Friday, Jan 15, 2010 at 20:46

Friday, Jan 15, 2010 at 20:46
I've just recently purchased a Battery Monitor-clm from OEX through my local Auto Sparky. About $130.00 but worth it.
Unfortunatley their site is down for maintenance ATM OEX
You can use it on deep cycle as well as dual purpose batteries as well as your normal vehicle battery.
It shows
1; Charge level
2; Battery life
3; lost capability
4; recharge level
5; Volts
It needs resetting for each battery you use it on, which is only a matter of putting a pin in a slot to reset it.
Just recently I found the old girl struggled a bit to start. Clipped this to the terminals, waited 30 seconds and it showed 24% charge level with 12.7 volts. So I took the vehicle to an auto sparky who tested it while the engine was running, and under cranking load, and said 'Yep shes stuffed and on the way out'.
Took the battery back to the supplier and it was replaced under warranty.
I know 130 bucks seems a lot, but I can check any battery that I have.
And with more and more demand put on our batteries this helps to monitor them

AnswerID: 399631

Reply By: ABR - SIDEWINDER - Friday, Jan 15, 2010 at 20:51

Friday, Jan 15, 2010 at 20:51
Hi ss--ss

If you know the battery is in good condition and not suffered any damage from sulphation etc. You can then use the voltage method at rest to check the battery SOC.

If you don't know the condition of the battery then you should load test it as suggested. I find using a 50W down light drawing 4A is a good way to test a battery.

Here is a graph to check batteries at rest.



Derek from ABR

AnswerID: 399632

Reply By: RV Powerstream P/L - Sunday, Jan 17, 2010 at 08:50

Sunday, Jan 17, 2010 at 08:50
If you know the battery is in good condition you shouldnt have to do anything and if you use loads to test them on a regular basis you are cycling he battery and shortening its life.

Battery Monitoring can be done in various wars but the simplest could be the one mentioned above as an OEX unit as it has similar characteristics to ones that come in three sizes up to 90A up to 150A and up to 300A but the existing importer only brings in the 90A unit which is generally too small and due to slow sales does not appear to be considering importing the larger units.

Although the larger units are available here in Aus. and are proving to be an excellent method of telling all the aspects stated in the earlier post .

They are called a "Battery Bug " by Argus of USA but made in Taiwan and the 90A is imported by Ashdown Ingrams being the appointed ditributoe for Australia.

Im not allowed to say who the firm is that has the larger units.
AnswerID: 399822

Follow Up By: Best Off Road - Sunday, Jan 17, 2010 at 09:37

Sunday, Jan 17, 2010 at 09:37

If you are the distributor/seller of Battery Bug or OEX you, as an advertiser, are entitled to say so.

This is from the Forum Rules

"A representative of any business may respond to any direct questions regarding the products and services they offer (but only if the user mentions your company or unique product/service)"

In this case a question has been asked battery monitoring and you have a unique product, therefore mentioning it is within the rules.



FollowupID: 668791

Reply By: R&J Batteries - Wednesday, Jan 27, 2010 at 15:40

Wednesday, Jan 27, 2010 at 15:40
Short answer is NO. Voltage is a very crude method of measuring battery capacity. State Of Charge (SOC) meter or a discharge test is the only 100% way.
You will get a "feel" for the battery charge with normal use over time if you look at the voltage on a regular basis. And never let your battery go under 11V to maximise its service life.

Dave (Fullriver Product Manager - Australia & NZ)
AnswerID: 401318

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