Battery Question

tnt · Dec 23, 2007, 11:09 AM

We have a Stowaway Type ST31DC205. 205 Reserve Capacity Minutes. 115 Amp Hours.

Which number should I use to calculate how long the battery will last?

I'm using the fridge to run a test on the battery right now. I want to see how long it takes to draw the battery down to 50%. The fridge pulls 10 amps. Starting with a fully charged battery, how long should this battery last?
Does anyone have a volt / % chart?

Tim5055 · Dec 23, 2007, 12:14 PM

Quote from: tntWe have a Stowaway Type ST31DC205. 205 Reserve Capacity Minues. 115 Amp Hours.
Which number should I use to calculate how long the battery will last?
I'm using the fridge to run a test on the battery right now. The fridge pulls 10 amps. Starting with a fully charged battery, how long should his battery last?
Does anyone have a volt / % chart?

I really would suggest stopping your test. The frige will draw it down in several hours and go below the 50% mark. At 50% you begin to damage the battery. 50% is only 12.09v DC, so be careful!

You can find a %/voltage chart on Mark's 12v Side of Life Web Page

Batteries on your Pop Up

tnt · Dec 25, 2007, 11:29 AM

About 3 hours got it down to 12.06V. That doesn't sound right for a battery this large does it?

Tim5055 · Dec 25, 2007, 04:12 PM

Quote from: tntAbout 3 hours got it down to 12.06V. That doesn't sound right for a battery this large does it?

Yup, it drains down quick.

tlhdoc · Dec 26, 2007, 08:10 PM

Quote from: tntAbout 3 hours got it down to 12.06V. That doesn't sound right for a battery this large does it?

Running your refrigerator off of the battery will drain it in a few hours, so yes it does sound correct, sorry.

tnt · Dec 26, 2007, 08:20 PM

Quote from: tlhdocRunning your refrigerator off of the battery will drain it in a few hours, so yes it does sound correct, sorry.

It's not that I run the fridge on 12V when dry camping, It's just that the fridge pulls about 10 amps. A good round number thats easy to use when calculating battery capacity.
Three hours at 10 amps = 30 amp hours. I just thought I should get more from a battery that claims 115 amp hours.

mike4947 · Dec 26, 2007, 08:25 PM

The problem is checking the voltage. It takes up to 5-6 HOURS after disconnecting a load for an accurate voltage reading. During that period it will rise up to the actual voltage. Any battery under load will show a drop in voltage greater than the actual amount. Try checking it again now that it's set if you have disconnected it so the phantom draws haven't dropped the actaul voltage level.

pricerj · Dec 31, 2007, 04:45 PM

As an engineer I am somewhat embarassed to ask... but why does a battery have such a high voltage reading when it is fully discharged? I mean, shouldn't the voltage drive towards zero, not just a few volts below 12v?

(I took 4 Electrical Engineering classes in college, 3 were the same class....)

tnt · Jan 01, 2008, 09:45 AM

I attached it as a pdf. I hope this works.

tnt · Jan 01, 2008, 10:56 AM

I found the paperwork that came with my Stowaway deep cycle battery!
I tried to attach it to my reply as a pdf. but I could not make a readable pdf. under the 40kb limit. If anyone is intrested, send me a email and I will send it to you. I would like to thank everyone for their help. Have a Very Happy New Year!

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