Second Battery Fault

The only way to test the capacity of the battery is to remove it from the car, charge it up using a multi-stage charger, then discharge it using the current the manufacturer tested the battery at.

My crude method was to run the fridge off the battery and record the voltage periodically. You can then gauge roughly what the capacity is. If you are still only getting 10 hours from the battery, then it is time to replace it.

[Wherever I May Roam]

mjrandom, last time i volt tested the battery i think it was about 13.5v and the reading from the anderson plug and fridge plug was the same, have never used the anderson plug and fridge plug at the same time but will be rolling out the new campertrailer this long weekend here in Perth to see how it goes. As for the fridge i usually run it at 2C and keep it as full as possible as i was told this helps the fridge out. Do you have any advice on testing how much the fridge is drawing?
Cheers

[ScoticusMaximus]

maybe also check the battery type, i recently discovered i wasnt giving my battery enough charge, it is a calcium type so it needed a higher input that the charger i had wasnt providing

[mackayvx]

Try giving the battery a good boost charge...
I was having problems similar to yours and I found my battery was constantly flat...
Whenever I go away I charge both my batteries overnight with my 20amp multistage charger and I haven't had a problem since.
Daily driving for a few hours whilst I'm away is plenty to keep to battery topped up... And that's running a 78ltr ARB fridge.
Quite often I take my charger with me if I'm away for more than a few days so I can boost charge them overnight if I'm near a power source.
I used to have a lot of dramas with this kind of stuff but now I take a proactive approach and I haven't had a problem.

[mjrandom]

Hmmm not really enough information. How much charge is in the battery? Agree you probably need the LeighW diode if the megatronics is an isolator system. What size wire is running from the battery to the fridge? You may be losing a lot of Vs without even using it. As for the fridge it depends how full it is, what temperature it is set to, how many times it is opened, how hot it is in the car. Does the fridge have a low voltage cutout and what is it set at, and so on.

The other thing to keep in mind is if you have a fully charged 110AH battery you probably only get 50 or 60AH out of it without damaging the battery by taking it too low.

The fridge will probably draw about 4A and run for 20 to 25 minutes per hour on average if it is reasonably full and set to 0C. So somewhere between 25 and 40AH per day. Again depends on how hot it all is. I have some readings from my NL 50L weekender somewhere on here and I think it was about 16AH minimum to about 28 maximum depending on rainy day versus red hot day.

So I would think that you might have a couple of issues, the battery is probably not as fresh as it could be, you are probably not feeding it enough volts to keep it fully charged and you may be losing some voltage in the cabling.

1. How was the battery load tested? It sounds like the battery is knackered based on my own experience where my 130Ah battery lasted only 8 hours. It was properly load tested with a constant current draw and timed
2. You might need a voltage booster diode for the diesel Prado to up the voltage on the alternator (PM LeighW)

[Wherever I May Roam]

Hi all, just wondering if anyone could help me out. I'm not that great with solving electrical issues hence this post. My dual battery system was already installed on my 2007 GXL when i bought it 2 1/2 years ago, whilst i only run a second fridge off it when we go camping it seems to be dying too quick. The advice i have received thus far is varied, 110 amp hour battery, 40l waeco fridge- everyone has told me the basic rule of thumb is on average the fridge will draw approx 2 amps hour so it should give me approx 50 hours of battery without charging/driving. The problem i have is that the battery is dead after about 10 hours so the diesel generator (Prado) needs to be run for a few hours to keep it charged. I have had the second battery "load tested" and all says the battery is ok, so my question is what are the best methods to DIY this myself. The way i see it a. the fridge draws more than the suggested 2 amps b. the battery is stuffed or c. the dual battery system doesnt work weel enough. The dual battery system is one ive never heard of its called "megatronics". Any suggestions would be appreciated. Cheers