Mark replied:

Michelle,
I installed an Exide Extreme (80ah) battery as an auxilary to run fridge etc. Its a starting battery but has thicker plates like a deep cycle so can handle cycling better. Batterys about 2 years old now and going strong so seems to be up to the job. I have no doubt the Optima is more suited to deep cycling as this is what it was designed to do, but at $400 vs $150 i'm not sure the difference is that great. Most modern fridges cut out before the battery is totally flattened anyway.

Nigel replied:

if you are using a parallel charge system like piranha's then you shouldn't mix battery types. With an independant charge system, where the batteries are never connected together, you can use a starter battery and a deep cycle. One reason why many people avoid deep cycle batteries is coz the cheap ones are made for stationary applications and fall apart in a 4WD. Well made batteries like Federal, Trojan and Optima overcome that problem (but be aware that the optima is on 55 Amphour). Another problem with deep cycles is that they don't charge properly from a alternatoras they prefer a slower charge at a higher voltage. I opted for a Federal 105 Amphour for my second battery and use the Rotronics independant charge system. I use an Arlec DC10 (10 amp RMS, 6 amp DC) to top it up after every trip. The system was installed by opposite lock for around $400 (not fitted) and the battery purchased from battery world for $250. The tray was installed by opposite for $250. The Federal runs our EvaKool 70 litre fridge for a long weekend without having to start the car. Another option would be the Century MarinePro 600 battery which is a starter battery with more tolerance for being discharged then most starter batteries, but you will still get a reduced life if you discharge it more than occasionally.

Jim replied:

Michelle, I tried for months to sort out dual battery systems. Each person I soke to has a different story. I'm not sure I've got the correct answer - maybe there ain't one. On the basis that batteries suffer sulphation if not reharged fully fairly quickly after draining, I've wound up wiyh a cranking battery and a deep cycle battery. All the systems run off the deep cycle one, and a solenoid is used to isolate them. There is also a switch that will isolate them when engine running, with the object of directing the full charge of the alternator to the deep cycle battery. I am also to charge the battery fully using a charger after each trip, and to watch the state of the batteries by measuring the SG every 3/12 or so. I am told that will ensyre long life. For what it's worth, there gas been no loss of SG since put in in July 2001.
I wish you the best of luck in trying to sort out what appears to ne to a dog's breakfast!

Goran replied:

Michelle, it all depends where you going and how long you staying at one place.If you decide to go for deep cycle look into overlander range. They are excelent.Be aware that deep cycle batteries are not designed to be used for starting.Use to start only when you have to as prolonged starting use will kill it. If you are prepared to spend 1100 bucks you would be better off with another starting battery and new Honda generator UI 1.0 KWA. More bang for your dollars.
Cheers

paul replied:

Michelle

Just to correct one perspective up above, the amazing thing about the Optima yellow top is that it has a cold cranking ability the same as most starting batteries. But better still unlike most other deep cycle batteries which are wet batteries and can only be charged at around 10-20% of their Amp hour rating (ah), the Optima can take a very fast charge. That is an 80 amp hour exide deep cycle battery may last longer than a 55amp hour Optima but the exide will take all day to recharge whereas the Optima can be charged from flat in about an hour - if you have a charging system that can charge it that fast. I go camping with an explorer fridge freezer, if i am stationary i can recharge the optima off a Les Christie battery charge for about 30 min in the morining and about 30 min in the evening.

Tom replied:

Michelle
Here's a different angle to consider. Get a three way fridge - overnight and for as many nights as you want it will run on gas!! No need for a second battery. Your normal battery will run your lighting. Oh and don't be put off by people who say they don't work well. All caravans have gas/electric fridges and they travel the length and breadth of Australia without a worry!!!

Howard replied:

I look at what some people spend on dual battery systems and now i know why the vehicles never leave the tarred roads. (they cannot afford the fuel after paying thru the nose for a dual battery system).michelle , fit a deep cycle battery with a manaul isolator switch.should cost about $250 in total.i have used a 75 amp hr deep cycle battery for over 3 years in a 60 series diesel and is now fitted in my 80 series petrol. runs the fridge ok and cranks as well , to the extent that it was only after a long weekend fishing trip that i discovered that the main starting battery was RS and the deep cycle had been turning the old 2H diesel over thru the canberra winter with plenty of below zero morning starts.
sure you have to open the bonnet and wind the green knob each night but even with the current price of fuel you are hundreds if not thousands of km's ahead.

Howard replied:

I look at what some people spend on dual battery systems and now i know why the vehicles never leave the tarred roads. (they cannot afford the fuel after paying thru the nose for a dual battery system).michelle , fit a deep cycle battery with a manaul isolator switch.should cost about $250 in total.i have used a 75 amp hr deep cycle battery for over 3 years in a 60 series diesel and is now fitted in my 80 series petrol. runs the fridge ok and cranks as well , to the extent that it was only after a long weekend fishing trip that i discovered that the main starting battery was RS and the deep cycle had been turning the old 2H diesel over thru the canberra winter with plenty of below zero morning starts.
sure you have to open the bonnet and wind the green knob each night but even with the current price of fuel you are hundreds if not thousands of km's ahead.