why can't it be simple?

Submitted: Monday, Jul 12, 2004 at 23:00
ThreadID: 14610 Views:2038 Replies:3 FollowUps:3
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With under bonnet, deep cycle aux batts what is the recommended (if any) maintenance schedule in between trips. e.g 3/4 mths at rest. Is it a set and forget item?

What is fully charged voltage? What is flat voltage?

Any simple ideas on what to plug into the rear aux socket to give the aux batt something to do while about town. Wanted to keep it cycling etc. Didn't want to keep fridge in 24/7.

I know I can check the archives but my eyes are straining and I'm feeling lazy tonight.

thks in advance
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Reply By: Magnus - Monday, Jul 12, 2004 at 23:16

Monday, Jul 12, 2004 at 23:16
Check this site



AnswerID: 67544

Follow Up By: Member - John C (QLD) - Monday, Jul 12, 2004 at 23:26

Monday, Jul 12, 2004 at 23:26
Cheers Magnus
but been there done that
good site
that's what got me on the subject
but need simple answers to simple questions
FollowupID: 328237

Reply By: V8troopie - Monday, Jul 12, 2004 at 23:37

Monday, Jul 12, 2004 at 23:37
John, deep cycle batteries come in 3 common flavours.

1. the wet cell battery, you have to keep a regular check on the electrolyte level and top it up with distilled water. Some brands are more thirsty than others, the Trojans I had were real guzzlers of water.
You have to keep the battery charged, leaving it discharged for any length of time will reduce its life drastically. See the site suggested in the other reply for your voltage measurements. Keep in mind that due the small difference between full and empty you need a digital voltmeter ( or multimeter set to read 0-20 volts - they are under $20.- now). Do not measure unless the battery has been sitting there doing nothing for some hours - you get misleading readings if you measure just after you turned the engine charging off.

2. the sealed wet cell battery, as above minus the water filling bit (since you can't do that with these batteries)

3. AGM batteries, Gel batteries - I have never owned any so check the website for info.

There is NO need to give the aux. deep cycle battery something to do just for the sake of it! Any charge you drain out has to be replaced plus interest (for losses).
Deep cycle batteries have a finite number of charge cycles, dont waste them!
The number of cycles depends how deep you discharge the battery each time - if you discharge it down to 10% capacity you get very few cycles. If you discharge it only to 70-80% of capacity you get LOTS of cycles.
If you use the car regularly and the battery gets regularly connected to the alternator (via a relay, etc.) you need do nothing at all while about town. If you park your car for weeks or more, get a small solar panel (~5-10watts) and leave that connected to the battery, making sure there is some sunlight to the panel for several hour a day. You need no extra regulator for these small panels connected to a large (70+ Ah) deep cycle battery, just a diode at the panel to prevent dark discharge.

AnswerID: 67546

Follow Up By: Member - John C (QLD) - Tuesday, Jul 13, 2004 at 00:46

Tuesday, Jul 13, 2004 at 00:46
Thks Klaus
apprec that

The battery is a sealed wet cell and i have a meter connected which shows voltage.

Unfortunately I live close to work less than 5 mins drive, and most trips during the day are short 5-10 mins, don't know whether this is doing any good or not. I think the management system will only switch over from the main batt after 4/5mins approx, I have to check with supplier, it may share to both during 1st 4/5mins.

The voltage meter will read over 13 after say a 15 min drive but overnight settles at about 12.6

when away, I run a fridge & it will drop to 11 'ish volts after 2/3 days. I think I read it shouldn't go too much lower before it needs to be recharged.

Anyway sounds like I should be OK as is.

FollowupID: 328241

Follow Up By: phil - Tuesday, Jul 13, 2004 at 16:13

Tuesday, Jul 13, 2004 at 16:13
I totally agree about this furphy that deep cycle batteries need "something to do" I wish people would not keep repeating it! It gets even sillier when people run a flouro lamp all the time, as well as having the battery on a trickle charge such as a solar panel at home. All that is doing is reducing the total charge from the panel. Much better to regulate the panel.
What deep cycle batteries do not like is over charging so you need to make sure that your vehicle charging voltage is correct. If there is a lot of water loss this is a possibility.
Phil I
FollowupID: 328280

Reply By: V8troopie - Tuesday, Jul 13, 2004 at 22:19

Tuesday, Jul 13, 2004 at 22:19
John, 11ish Volts at the battery terminals sounds bad, very bad indeed. If you measured that while the fridge was off for a while, I would say the battery had it.
If the battery was getting on in years you might measure under 12 Volts while the fridge was running and the battery is about flat, due the batteries higher internal resistance.

I would take steps to recharge it when the terminal voltage drops to 12.2 V at the latest, running it lower than that shortens its life and it takes absolutely ages to get it fully charged again.

Your 12.6v at rest is fine - battery is fully charged. The voltage should not get higher than 13.8 - 14v during charging but if you measure much less than that it's not getting properly charged.

If you run a fridge with a swing motor (Engel) then the lower voltage makes the fridge work ever harder since the compressor will not make the full stroke any more. It gets to the point the fridge is running just about constantly, killing the battery even quicker. Rotary compressors are more forgiving to low battery voltages.

Sorry, its not a simple subject by any means, especially for someone to whom electricity is unfamiliar territory.
AnswerID: 67681

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