Deep Cycle Batteries - Charging

Hi Vcbb

Takes a good low resistance setup to charge from car only, but its achieveable.

Is 2nd battery in car or a camper ?

Best is always a step up charger (like CTEK) from car system for travelling when battery is located far from main battery.

The more the better, but even the lower output 7 amp types work well and wiring is less critcal.

Robin Miller

You need to hook up second battery to main one with good thick cable, as least 4G to make resistance minimum and charge it properly. If you are using some kind of isolators then keep in mind that electronic one have voltage drop about 0.5V. You can compensate against it, but then main battery became overcharged. And so on. If you using deep one just for running fridge, particularly in caravan, I would rather use inverter and good charger like CTEK to charge it. Or if it under bonnet put good cable between batteries and if in doubt put good mechanical switch between them to separate them overnight.
Cheers

For charging on mains anywhere, any of the quality 3-4 stage smart chargers should suit - designed to connect and leave for the duration - when full they go to float mode - they have a selector switch for gel and/or wet types. More $ = more current = shorter charge time it seems. http://www.sidewinder.com.au (advertises here) is one source of tech advice and prices.

Hi VCBB - also worth taking a look at Collyn Rivers site - explains the issues in clear simple language :
Here is the site :http://www.caravanandmotorhomebooks.com/articles/index.htm

.....................Keith

A few things could be limiting the charge getting to the deep cycle. The distance to the rear of the car requires a fairly thick run of copper & should include a negative wire not just earthed to the body. In many cases it can be something as simple as a poor connection. Charging two dissimilar batteries can often see the start batt recieve charge quicker so over short drives in particular a deep cycle may recieve little. Depending on your duel battery system they too can divert charge to the start batt first & when they reach a predetemined voltage only then does the deep cycle get anything. The amount of charge available may be a bit low as well if the altenator is an older small amperage unit & you have heaps of assesories running. My Hilux for example only had a 55 amp altenator & if I ran the stereo & all the driving lights at once the batteries would go backwards.
I have had no problems charging deep cycles for 25 years even used in conjuction with a start battery so I'd suggest there may be some other issues causing your problem, I wouldn't be blaming the battery just yet.
Out of intrest how are you measuring if it is at full charge & what % do you think it gets up to after a couple of hours drive?
Cheers Craig............

I was at the Opposite Lock shop today and was reading the data on the the Rotronics dual battery system. I have one of these systems and did have some trouble with charging my batteries when I was running two fridges (one fridge, one freezer) on my Canning Stock Route trip. What I learnt was that you can have a Parallel connection or an independant connection. Most are parallel (cheaper). This charges both batteries at the same time but will only charge your deep cycle battery to 90% capacity. An AGM battery will only be charged to about 85% capacity. A deep cycle battery that has been 90% discharged can take as long as 8 hours to recharge. With an independant connection the cars battery is charged first and then the second battery is charged. This connection will allow your deep cycle battery to be charged to 100%. They recommend this connection for AGM batteries and can charge one of these to maximum charge in 2 hours. I wish I had known this when I was setting up for my trip. I ended up with the parallel connection with a deep cycle battery. Where as I really needed an independant connection with an AGM battery to keep up with the power drain. Hope this helps.

Garry

Hi vcbb, are you enjoying all the fairy tales being posted about how you batteries aren’t going to be fully charged unless you spend lots of dollars, all because your alternator can’t fully charge your battery.

I’m sorry but most of this misinformation is total MYTH.

For a start, if your battery is not fully charging, the two most common causes are the battery cables are too thin and/or you not driving long enough to allow the battery to charge.

Neither has anything to do with the ability of your alternator to be able to charge your deep cycle battery to at least 95% and I say 95% because it is almost impossible to determine if a battery is 100% fully charged without removing the battery from the vehicle and taking it to a laboratory to have it analysed, not exactly practical.

Now whether you believe what I have posted is correct or not is up to you but contrary to all the so called experts that claim, for what ever reason, that your alternator will not fully charge a battery, start by checking what the real battery experts say.

By real battery experts, I’m talking about the battery manufacturers. Find one battery manufacturer that states that their automotive battery can not be fully charged by a vehicle alternator.

Before you go spending a fortune in an attempt at fixing the problem of your deep cycle battery not charging properly, do a fair bit of research first

When you get the correct info you will see it’s not going to cost you very much at all to permanently solve your problem.

Again, any battery, cranking or deep cycle, intended for automotive use, an be fully charged to at least 95% by the vehicle’s alternator, IF the vehicle is set up correctly in the first place.

This has generated some very good discussion. To clear up my story a bit:

I have an opposite lock battery box, which was supplied very thick cable (pos & neg) to run from the engine bay, and all the bits and pieces. Perfect for the vehciles with no room in the

The main battery is provided with charge first, then when fully charged ((based on voltage), the second battery is charged.

Most of the days we were driving was for 5 - 8 hours, so it was getting many hours charge.

I thought, that Deep Cycles only accept a trickle charge..... is this true or does it accept full charge from the alternator???????

Towards the end of the trip , from Townsville to Laverton, ( 6 - 8 hours per day), I noticed, that on the battery display in the cab (OL dual battery monitor), that when stopping the battery went down to 50 - 70% after only a couple hours, and this was different behaviour from the first few weeks of the trip. It didnt appear I was getting as many hours out of the battery. It had been drained a couple of times to zero during the trip, so I am thinking this may have some affect on the battery.

If a wet cell Cranking battery is 12.6 Volts, about 3 hours AFTER being driven, it's fully charged.

If a Solar system or battery charger is not connected, it must have been the Alternator :-)