Second battery needed for fridge

Yep!! I tend to agree, just dont drain them too much and they last to a normal life.. Michael

Also yep, what signman said. Cranking battery will work fine, it has done for me for years.

yep and they charge faster compared to a deep cycle

yes Cranking batteries WILL charge faster than all Deep Cycle battery that's a known fact, reason being they have thinner plates and do not have the continuous high drain cycling advantage of Deep Cycle batteries.

Cranking batteries can't be drained as low as a Deep Cycle batteries according to every battery manufacturer's web sites on the net or the various battery 'information' web sites either.

The most effective battery to run a fridge is an AGM Deep Cycle, as it will recharge much faster than any Cranking battery and cycle even lower than any wetcell Deep Cycle battery, but yes they do cost more, so if you want a compromise use something else, however if you want the BEST performance from an Auxiliary battery get an AGM Deep Cycle battery.

Anyone who has used an AGM and found it unsatisfactory please state the perceived reason and the charging/battery system specifications...

Hey Gossy
You sure you can keep flattening a 'deep cycle' battery- and expect it to keep charging full, with max. output???

I'm with Signman - Most wet cell deep cycle batteries only come with a 6 month warranty .....for a reason!

you will kill any battery running them dead flat. Deep cycles are no exception

Leroy

"Most wet cell deep cycle batteries only come with a 6 month warranty, for a reason" and the reason is ??

Quality wetcell DC batteries have a 12 month warranty, Cranking batteries have a 2 year warranty because they are ONLY used to start cars, not run as Deep Cycle batteries.

Quality AGM Deep Cycle batteries have a 10 year life expectancy, my previous Delkor Deep Cycle batteries lasted 4+ years when I replaced them, I gave one away to a guy who needed it more than I did and replaced my 4yo overlander 700cca Cranking battery with the other, that Deep Cycle battery has been used for 13 months as my Cranking battery and is now over 5 yrs old.

I replaced the Deep Cycle delkors with 100+ ah AGM's and had them tested only last Saturday, they were producing in excess of 1,200cca and easily passed the Deep Discharge testing applied to them by their supplier.

Dead flat is often stated as being 12v, however most battery isolator switches and fridge cut-out systems are set for around 10.5v to 10.8v which is well below what the battery is designed for, constantly running batteries to this low level cause the battery to die prematurely, as has to be expected.

Mainey, the dead flat at 12v you mention, is that under or off load ? Obviously the cut-out voltages 10.5v to 10.8v must be under load but at what current draw. My fully charged cranking battery drop to around 8 volts when cranking but recovers almost immediately.

No load....12v is dead, however can often be recharged.
Yes the 10.5v figures are under load, however the load would only be about O.4v
My "power hungry" fridge draws ~10Amps (running) and only drops my voltage O.5v.

Your Cranking battery drops to 8v only because it's built to use a massive power drain only for a few seconds when starting the vehicle, and yes it recovers immediate because either the alternator recharges it again or the natural battery acid reaction returns it to 12.6v that's what happens in a healthy battery.

Mainey,
The "reason" most wet cell deep cycle batteries ONLY come with a 6 month warranty is the way they are used and abused, as a second battery under the bonnet of a 4wd.

If you repeatedly do what Gossy suggests (discharge to dead flat), then you'll trash the battery. In addition, because they recharge slower, they are less likely to be recharged by a vehicle alternator to a reasonable charge state in a short space of time, so they sulphate.

Phil,
I used the word "quality" – yes some 'budget priced' DC batteries may only have a 6 month warranty, however better "quality" built batteries that cost more than the average low priced battery do have a better warranty and do give superior service and most quality built AGM’s actually have a 10 year life expectancy.

You will only get what you are prepared to pay for.

Yes, a battery will sulphate when it sits with no charge applied and while in a very low state of charge for any reasonable period of time, which equals low battery maintenance, not by discharging and charging often and fully.

No battery will be abused IF the battery "system" is correctly set-up in the first place.
My own system has never been seen below 12v at any time, day or night, it's just a matter of having the correct sized capacity battery / batteries, cabling, auto battery disconnect system and most importantly recharging system available.

I draw only of the top of my ~2OO+ ah Auxiliary battery system, if it was of lower capacity obviously I would drain it deeper and more often, which would shorten the useful life of the battery. My first Deep Cycle battery was an American made mega expensive failure, simply because it was only 90ah and it drained to far & too often, it only lasted about 3 years.
My next system was 2 x 80ah, they lasted 4 years and I replaced them, not because they were small or faulty simply because they were 4 years old, I now use one of the batteries as my Cranking battery and its been doing that job since March 2006 when I replace them with 2 x 100+ ah AGM’s.

Because I choose to camp in one place for weeks at a time without driving the Aux battery system has to be fully self sufficient in capacity and also it’s recharging system and basically because I’m lazy I use Solar as the recharge power source.

Those who only rely on the alternator to recharge their Auxiliary (often only 1 & also undersized) battery should not expect to get the same life or performance from their Auxiliary battery system as those with fulltime recharge facilities available for their Auxiliary battery system.

Hmm, then how come cranking batteries do such a good job of powering a fridge ? is it because a fridge switches on and off, not demanding constant power ? My cranker (exide extreme) which is used mainly for the Engel is still good after two years, it also charges a lot quicker than my previous deep cycle.

Red Frog
What else do you run of it apart from fridge, try running camp lights (fluro,) laptop& GPS, radios, diff lockers and you will find the average cranking battery can't withstand the demands. Fiona may not be running anything else apart from fridge at moment but as you know you soon start adding things to the truck that require power as well.

Thanks Bentaxle, I'll keep that in mind.

generally Mike when you are running the laptop, gps, radios etc you are using your vehicle so not really an issue ie engine running and you're driving around.
Don't know about the battery operated diff locks though. They may draw a lot of current while stationary over night!
Using a fluro only draws around 1ah so not a big burdon on any batt.

Leroy

Marine batteries are 'different' only because of the method of "attaching" the plates to the case... to avoid damage caused when the plates vibrate around in a boat, which is much rougher than in a vehicle.

My 5 yo Delkor Deep Cycle batteries are Calcium.... lol

As to measuring the voltage of a battery that has recently run a fridge for 24 hours it has to be expected it would be 12v not long after the fridge has stopped, however if RE-tested about 2 hours later it would then read in excess of 12.5v

If the battery is 12v some hours after running the fridge, it's close to dead !!