ARB surepower solenoid

Andrew
most fridge cutouts are designed to protect the compressor and cut out way too late for battery protection.
A deep cycle battery needs to be run down/utilised consistently and not on say, a once a fortnight/month camping trip, which is the hard part. I was chewing through a battery every year but have since changed to Rotronics system and my Century Marine Pro is still going strong after 2 years now. Have friends who are in their 4th & 5th years of same battery after installing Rotronics and one who just lost his after 8 1/2 years (one of those fancy Orange suckers - can't for the life of me think of the name but I'm sure it'll come to me as soon as I submit this post).
I have since upgraded my car sound system and run 2 amplifiers off my aux battery so think I can move to deep cycle next purchase as this will run it down regularly.
I'm no expert and these are my thoughts only but hopefully they will help.Allyn
Where to next ?

Andy,
Looking at the Surepower info, you have a diode isolator, rather than a solenoid isolator. This means that the diode feeding the battery with the lowest charge voltage will tend to stop the diode feeding the other battery from conducting till the voltage on the lowest battery has risen sufficiently (the diodes don't conduct till they have 0.2 - 0.8v across them, depending whether they are shottky diodes or normal silicon diodes); ie, the poorest battery gets charged first, but this doesn't necessarily mean the biggest or smallest gets it first.
This brings us to the next point, which is that there is a finite voltage drop across the diodes, which may prevent the alternator delivering the full 14.2v to the battery, perhaps accounting for why the battery is not at sg 1300. The Surepower spec sheet doesn't say, but chances are your diode isolator has silicon diodes, which drop about 0.8v, so a 14.2v alternator may only deliver as low as 13.4v when used with the above.
Some alternators have external sensing for the alternator regulator (eg, Nissan Patrol) which corrects for this, but many alternators have a fully integrated regulator, which means you lose out.
Re battery choice, there are many postings on this website. I used a cheap deep cycle Exide, and got over 2 years of hard work out of it (with a solenoid combiner) and it only died coz someone switched off my battery charger while I was away overseas. I now have an expensive Trojan battery, and 9 months down the track, it's looking sick.
Lead acid batteries, unlike NiCads, prefer not to be fully discharged, and the shallower the discharge, the longer the life. If they are fully discharged, the quicker you can get them back up again, the more chance they have of surviving, as prolonged periods of discharge ruin them.
If your fridge has a Danfoss compressor, then the low voltage cutout is 10.5v, restoring at 11.5v. This should not cause serious damage to your battery if it drops to this, but you would be well advised to bring the charge back up again soon after.
rgds
Gerry