How long will my battery last

Submitted: Thursday, Jul 17, 2003 at 22:14
ThreadID: 6034 Views:3695 Replies:5 FollowUps:5
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Guys, How can you work out how long my second battery will last with my fridge hooked up to it. I have just purchased an Optima D34 battery. On recommendation from the product reveiw Aug issue. This battery has a storage capacity of 55AH ?? & a discharge capacity of 600 cca ??. This is fitted into a Piranna duel battery management system. How long approx would it last with the Weaco 35lt running & with no other major draw.
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Reply By: Member - Willem- Thursday, Jul 17, 2003 at 23:11

Thursday, Jul 17, 2003 at 23:11
I think that you have to divide the Amps that your fridge uses into the capacity of the Battery. In other words...if your fridge uses 2.5 Amps per hour running flat out then it should run on the 55AH battery for 22 hours before the battery is totally drained. That is my understanding.

Personally the fridge and I sleep in the same compartment so the latter gets turned off after lights out. Everythiong stays pretty cool inside the fridge through the night.Cheers, Willem
Never a dull moment
AnswerID: 25250

Follow Up By: GaryInOz (Vic) - Thursday, Jul 17, 2003 at 23:50

Thursday, Jul 17, 2003 at 23:50
Theoretically 22 hours, but practically (not letting battery get to less than 30-50%) about 14-16 hours. Absolutely no problem if driving every 1-2 days when used as you describe. Will need about 1-1.5 hours driving (over 2000 revs) to recharge.
FollowupID: 17084

Follow Up By: GaryInOz (Vic) - Thursday, Jul 17, 2003 at 23:53

Thursday, Jul 17, 2003 at 23:53
Correction: "...if driving every 1-2 days when used as you describe..." should be "...if driving every 1-2 days when used as Willem described..."
FollowupID: 17086

Reply By: Rod - Friday, Jul 18, 2003 at 08:20

Friday, Jul 18, 2003 at 08:20
Don't forget the fridge does not run continuously and it's cycling time is governed by the ambient temperature, the temp you have set the fridge to and the fridges ability to insulate itself.
So the way you "operate" the fridge can have a big affect on the car battery life !
AnswerID: 25266

Reply By: Mick - Friday, Jul 18, 2003 at 08:35

Friday, Jul 18, 2003 at 08:35
A waeco fridge should drag about 4Amps, flat out in 35 degree heat in the tropics, but in cooler climates or on lower settings there is such thing as dutycycle, where the thermostat cuts the fridge on and off for the required temperature.
At christie engineering we get 20 calls per day about the same problems.
An optima battery will be the best battery you can get, but there are larger types than the one you bought, which can run your fridge longer.
We reccomend running the fridge for 24 hours only as your voltage will be getting close to critical level. Anything below 11.6 volts, you will be starting to corrode the spiral wound plates. This is why we built our own battery chargers as you can recharge this battery in around 1 hour, then you have another 24 hours for your fridge, so you can camp in one spot for more than 1 day without stuffing your batteries.
AnswerID: 25268

Follow Up By: paul - Friday, Jul 18, 2003 at 17:57

Friday, Jul 18, 2003 at 17:57
Hey Mick

You may have noticed a very belligerent person that used to visit this site, apparently very knowledgeable but with an very abuse attitude, anyhow he was quite down on Les' charges because of the mating to an alternator, in his opinion this was a waste of power as the amp is were, as you note, controlled by the internal resistance of the battery. He advocated spending the money on a generator, even gave details of what to fit to a motor and how to achieve a constant say 15 amps in put etc.

Wonder what is your take on this type of opinion. thanks

by the way, i have the smaller christie charger and it does my job fine. though wouldn't mind selling it and getting the bigger model (do you take trade ins down there ?)
FollowupID: 17139

Follow Up By: Mick - Wednesday, Jul 23, 2003 at 08:48

Wednesday, Jul 23, 2003 at 08:48
Hi paul, the problem is with a constant 15 amps you can literally boil your battery, as when your battery is 100% charged and still putting in 15 amps is not good. Also not mentioned is the voltage, you could be charging at 12 volts or 20 volts, too high a voltage can boil your battery, too low wont charge it correctly.
There are too many answers, too many to list.
With your charger we can work something out, as many people are looking for a cheaper second hand model give us a ring on 02 9620 1208
hope to hear from you.
FollowupID: 17408

Reply By: Martyn (WA) - Friday, Jul 18, 2003 at 10:01

Friday, Jul 18, 2003 at 10:01
I worked it out for my Engle and it works diffrently every trip it's very much down to all the "other" conditions, amount of beer in the fridge, amount of times opened climate etc etc, the longest I have my fridge running on the battery alone without charging would be around 14 to 16 hours, or there abouts. As long as you air on the conservative side and you don't plan on not running the car for extended times you should be right. The theoretical answer will give you a ball park figure but there are so many other varients that dictate how long the battery will last before the auto cut out cuts in (mouthful) it would be very difficult to calculate accurately, this is only my opinion. When I go on a trip the performance of my battery improves with use, I run a small mechaincal clock in the back of the fourby to have a small constant discharge on the battery at all times, I've been told that leaving the auxillary battery doing nothing is very harmful, something to bare in mind. Keep the shiny side up
AnswerID: 25276

Reply By: Tony - Friday, Jul 18, 2003 at 11:41

Friday, Jul 18, 2003 at 11:41
My rule of thumb is pull up at a camp site around 4 in the afternoon stay the next day and move on the second morning and the fridge has run the whole time. Also a 12v light for about an hour each night.

Voltage on the aux battery still showing a tad over 12 volts.
AnswerID: 25288

Follow Up By: Member - Bob - Friday, Jul 18, 2003 at 17:15

Friday, Jul 18, 2003 at 17:15
That sounds like an excellent way to travel Tony. I wish I had the time to do it like that.
FollowupID: 17133

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