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Car Battery basics Part1

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2 years 5 months ago #51924 by juergen.scholl
There are several reasons, the most important one being that an AGM battery is considered to be fully charged or saturated around 12.8 to 13 volts. To reach this level of charge a higher voltage during the absorption charge is required. Absorption charge is the part of the charging process where typically the state of charge voltage is elevated from around 80% to 100%, fully charged. AGM batteries will show a memory effect over time - and loose capacity -when not charged correctly/completly.

An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
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1 year 6 months ago #57933 by trjp
Replied by trjp on topic Car Battery basics Part1
Some really interesting stuff here - thanks for sharing!

I've become a bit obsessed with how a regular lead-acid batteries deal with low-amp drains because I kept coming across people saying things like

"It's a 65AH battery and there's a 250ma drain so it will take 260 hours to drain"

Sadly that's not remotely true - that 65AH rating means it will supply 3.25A for 20 hours without dropping under 10.5V but that doesn't mean it will supply .325A for 200 hours or 7A for 10 hours - batteries are not buckets of electricity, it's more complex...

I also believe that a varying load drains a battery faster than a steady one - e.g. switching between .5A and .1A will drain a battery faster than a steady .3A - but I'm finding that one hard to test/prove!!
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1 year 6 months ago #58258 by Rupert S
Replied by Rupert S on topic Car Battery basics Part1
Here is something that will make you a laugh.
The battery rep that comes round to us told my boss that a battery will start on a different cell each time you start the car. So if you have an intermittent starting issue it could be down to a bad cell!
He seemed to think that the current started flowing from a different point in the battery on each start up.
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1 year 3 months ago - 1 year 3 months ago #59070 by In My Garage

Here is something that will make you a laugh.
The battery rep that comes round to us told my boss that a battery will start on a different cell each time you start the car. So if you have an intermittent starting issue it could be down to a bad cell!
He seemed to think that the current started flowing from a different point in the battery on each start up.

Exactly why I do not listen to people in sales or marketing because they are repeating things they heard somewhere (much like on forums) but have absolutely no background in science or practical engineering.

On one car forum I am on, there was a battery rep advertizing "The Last Battery Charger You Will Ever Need". A $100 unit built to a price point. Anyway, the charger also performed a Load Test. So I asked the rep "what is the load current". It took a while (because he didn't know what a load or current is) and gets back to me with 20W. That is less than 2 amps current draw. Wow, that is one hell of a load test. Of course you get quite unpopular with some forum members because they bow at the ankles to these reps and they want to "believe". LOL
Last edit: 1 year 3 months ago by In My Garage.

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1 year 3 months ago #59071 by In My Garage
Unless you know, people have no idea what battery capacity is. It is best to relate to something most can understand.

I've often related it to people by using two vessels; a kitchen sink and a swimming pool, both filled with 12.6 inches of water. Each inch is equivalent to 1V.

Now open the 1" diameter drain hole in the bottom of each vessel right above a turbine wheel which is capable for doing work (your starter).

You'll notice the kitchen sink being down to 6 inches in no time whereas the water in the swimming pool hardly changed its level. As the water level drops, the flow pressure drops to the turbine (your starter) as well...

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1 year 3 months ago #59072 by In My Garage

I also believe that a varying load drains a battery faster than a steady one...

When a capacity is stated on a battery, it is done at a certain C rate.

Too many people think that a 100 Ah battery will supply 100A for 1 hour or 1A for 100 hours.

Time to read up on Peukert's Law.

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11 months 3 weeks ago #60847 by Leon
Replied by Leon on topic Car Battery basics Part1
Nice

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11 months 3 weeks ago #60851 by MarkBeck101
The impedance battery testers work best when the battery is out of the vehicle or you can gain access directly to the battery posts, which is not always the case. For example, when the battery is buried in the trunk and the only access you have without first tearing apart the trunk are the jump start posts under the hood. The testers need to be at the battery posts to work.

The real advantage to using this type of tester is you can check the battery every week and plot its performance trend, that is a slow reduction in capacity with age and when it drops below 80% of the new installed CCA, you can recommend a replacement. This way your customer is never stranded even if they abuse the battery.

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