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walldoggie

gell cell battery

Question

walldoggie

seeing I am almost a complete (Contact Us Please) when it comes to elcetricity. I have a question about the difference between the 7 amp and the 9 amp vex batteries, other then the obvious of one has 2 more amps. The question would be why would you want one over the other. I only ask this question as i am going to be installing some lights and maybe a 12v dc adapter, in my portable. Thanks for all the help in advance. grin.gif

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Surface Tension

You'll get a little longer use out of the 9 amp hr battery. Say a MarCum draws 300mA. With a 7 amp battery you'll get around 23 hours of use. A 9 amp hr battery you'll get 30 hours of use.

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walldoggie

ahh ok, thanks

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PerchJerker

Amps or Amp Hours are measures of how much capacity is in a battery --- basically how much juice it holds ----- tells you which batteries are "bigger" and which are "smaller". More capacity, holds more juice, you get power for a longer period of time.

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MNbrewer44

Walldoggie

Go with the 9AH Battery.

The difference between 7 AMP-HOUR batteries and a 9AH battery is the capacity of the battery. The capacity of the battery is measured in AMP-HOURS. A 7-amp battery will deliver 7 Amps for 1 hour. The number of AMPS you draw depends on how many things you have plugged into the battery. I.e. A light rated at .5 amps will be able to run that for 14 hours. Each hour your light will draw .5amp. So after 1 hour you battery would have a capacity of 6.5AH. Now more then likely the lights you are going to install are going to be rated in mA (milliamps) or W (WATTS). So if you want to estimate how long your battery will last under a given load you are going to need to do some conversions.

1 AMP = 1000mA

9AH battery = 9000mAH

Eq 1.

Hours = (mAH of battery)/ (total mA draw of equipment)

(9000mAH)/(500mA) = 18 hours

Now depending on what kind of lights you use they may also be rated in mW or milliwatts.

Eq 2.

To convert mW to mA use this formula:

milliamps = milliwatts/Volts or mA=mW/Volts

So if your light is rated at say 400mW

33.3mA = (400mW/12V)

Use the mA load you calculated in Eq 2 and plug it into the Eq 1 to determine the duration of this light.

*Unfortunately AMP-HOUR is not always a good way to determine the length of how long your equipment will stay on. Manufactures are not required to and do not all use the same duration of time when measuring the discharge. It is usually right around a hour however companies can vary by large amounts. So one 9AH battery may last longer then others. So if the batteries you are looking at are from the same manufacture they will be measured on the same time duration. For this reason the above equations can only be used as an estimate. Only trial and error or a specific amount of time the manufactured used to rate the battery will give you a precise answer to how long your equipment will stay on. Also age of battery will affect this.

I know this isn’t exactly what you asked but I thought it might help you see the difference between the two batteries.

Hope this helps

Brian

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Deitz Dittrich

Dude.. great post.. my brain just exploded! laugh.gif

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Whoaru99

Well, all that, plus....

The battery AH discharge capacity is less when the battery is cold and the colder it is the more the capacity is reduced.

If you want to get really deep, you can usually download all this information and the discharge curves, etc. from the batt. mfg. website.

For example, I have some Panasonic batteries in the 7.2AH capacity.

In order to get the 7.2AH rating, the discharge rate is over 20 hours so about 360mA or less draw from the battery to get the full 7.2AH. If one was to draw about 1A (1000mA) from the battery, it would give up only about 6.5AH.

With regard to the temperature, that 7.2AH rating is at 77F/25C. If you lower the battery temperature to say 5F/-15C, the capacity is only 65% or about 4.7AH.

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croixeyes

Ow!!!oww!!!my brain hurts...how long will it hurt at 4.7AH... confused.gif

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walldoggie

Now my next Question is where do i find the least expensive 9amp gel battery?

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TTfromBlaine

You guys crack me up grin.gif this fishin stuff aint is easy as everybody thinks blush.gif

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ice_it_06

Quote:

With regard to the temperature, that 7.2AH rating is at 77F/25C. If you lower the battery temperature to say 5F/-15C, the capacity is only 65% or about 4.7AH.


That is information most don't think about or are aware of with regards to temps affecting a batteries performance.

Without a full charge and warmer battery environment you are behind the 8-ball from the start !!

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