Battery monitor 12v reading amps

Submitted: Monday, Jun 02, 2014 at 22:09
ThreadID: 108074 Views:2111 Replies:5 FollowUps:5
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I'm looking for a battery monitor that measures amps in and out to get a battery state of charge,

I currently have 2 deep cycle batteries in my car and 2 in my lift off camper.
Does any one know how the monitor would go with accurate readings if I have all 4 linked together (to get charge from alternator while driving ) but when I setup camp and disconnect 2 batteries from the camper. Just not sure how it would read accurately
I would assume you would have to specify the battery sizes so when it's full it knows how many amps is has then remembers how much has been drawn out?
Just not sure how this works if some times you have 4 batteries in the mix and some times only 2

If any one can help that would be good
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Reply By: Echucan Bob - Monday, Jun 02, 2014 at 23:12

Monday, Jun 02, 2014 at 23:12

Ideally you would have two NASA battery monitors. If the budget doesn't run to that, you could have a single unit with appropriate switching. You'd need two resistor units though.

NASA Battery monitor

AnswerID: 533630

Follow Up By: John and Regina M - Monday, Jun 02, 2014 at 23:55

Monday, Jun 02, 2014 at 23:55
X2 for the NASA
Really the only way to do it well. Installation will b a bit of a pain but if u want to do it properly then u have no better options.

There r other ways, cheaper but nowhere near as good.
FollowupID: 817048

Follow Up By: Athol W1 - Tuesday, Jun 03, 2014 at 10:39

Tuesday, Jun 03, 2014 at 10:39
X3 for the NASA battery monitor.
Check out Ebay, they are quite reasonable and do a good job.
FollowupID: 817059

Reply By: The Bantam - Tuesday, Jun 03, 2014 at 18:06

Tuesday, Jun 03, 2014 at 18:06
You need to remember that a battery is not a bucket.

Its capacity is not fixed ( it varies with conditions and thru the life of the battery) and any notion of accuracy is an illusion.

The amount of current put in does not equal the amount of current out.

Even measuring "state of charge" using voltage is inaccurate unless the battery has been rested with no input or output for some time.

There are battery monitoring systems that claim to provide accuracy.....but if they are anything like affordable they are selling you snake takes a hell of a lot of smarts to account for all the variables.

simple straight forward digital volt meters with may be an ammeter in line is about as good as it gets...and that will only give you a vague indication.

AnswerID: 533669

Follow Up By: The Bantam - Tuesday, Jun 03, 2014 at 18:11

Tuesday, Jun 03, 2014 at 18:11
That NASA battery monitor linked above...while fine & beaut and a reasonable thing, will not provide accuracy.

it is a straight forward combined voltmeter and ammeter.....pluss an amp hour tracker.

Like many similar units, it will give you a vague impression of what is going on, but it will not give you an accurate measure of how much capacity is left.

FollowupID: 817078

Follow Up By: Freshstart - Wednesday, Jun 04, 2014 at 09:33

Wednesday, Jun 04, 2014 at 09:33
I agree. Current is not necessarily the answer. Voltage when working and on load is closer to the truth.

Put it this way and to continue with Bantam's analogy. A half full bucket will fill a glass with water just as quick as a full bucket will. How many glasses it will fill is akin to it's weight.
FollowupID: 817108

Follow Up By: The Bantam - Wednesday, Jun 04, 2014 at 15:41

Wednesday, Jun 04, 2014 at 15:41
just to continue with the analogy.

imagine a bucket that is in fact full (hwever you may draw that conclusion)......if that bucket is at its ideal operating temperature of arround 25ish is capable of delivering 100 units of stuff.

that bucket at 0C my be capable of delivering as little as 20 units of 50C it may be capable of delivering 60 units of stuff.

Oh and it gets more complicated...if you draw out of that bucket slowly, it will deliver a great deal more than if you draw from it fast.

as the bucket gets can deliver less but you have to put more in.

there are so many variables.

if you can get a fairly decent vague idea of what is going on you are doing well.

FollowupID: 817142

Reply By: Member - Scrubby (VIC) - Tuesday, Jun 03, 2014 at 18:26

Tuesday, Jun 03, 2014 at 18:26
G`day Mal,

I don`t think you will find anything as good as a "Xantrex LinkPro" for accuracy and quality.
Go here. (copy & paste) /

No affiliation with this mob, just a very satisfied customer.

AnswerID: 533671

Reply By: Slow one - Wednesday, Jun 04, 2014 at 16:20

Wednesday, Jun 04, 2014 at 16:20
have a look at the ABR sidewinder monitor. I have one and it is excellent and accurate. Simple install with anderson plugs so you can move it where you wish.

I have been monitoring my freezer over the last week and it records the accumulating amp/hour drain. Reset is easy, you just turn the power off and then on again.

To mount the unit velcro would be what you need.

Abr monitor link
AnswerID: 533737

Reply By: Peter Schrader - Wednesday, Jun 04, 2014 at 16:25

Wednesday, Jun 04, 2014 at 16:25
I like this one, I installed the shunt on the negative terminal of the house battery.

AnswerID: 533738

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