Battery minimum voltage without damage

Al,

Have a look at this site.

http://www.windsun.com/Batteries/Battery_FAQ.htm#AGM,%20or%20Absorbed%20Glass%20Mat%20Batteries

The accepted practice is to drain as little as possible out of it to extend its life. Apparently going below 50% (12.06 volts) regularly will stuff the battery quickly.

Cheers,

Jim.

Most of the available battery cutoff's kick in at around 11 volts or just below.
Most of the ones' in portable frigs operate at about that.
Operating any appliance below recommended voltage doesn't do it any good especially motors and refrigeration compressors, never mind the loss of efficiency.
Any battery is degraded every time you flatten it below a certain point.
Deep Cycle batteries supposedly handle deep discharge better than a cranking battery. Gel cells definately do.
Having had dual battery systems in 4wd's for over 25 years I'd suggest that lead/acid deep cycle batteries for the average 4wder are a waste of money, better to go with cranking batteries. If you want to spend the money you can't go past Sonneschein gel cells for aux batteries, I usually get a 10 year life out of them.
If going for cranking batteries the Korean ones are as good as any and have a 2 year replacement warranty. Which as yet I haven't had to use in over 10 years of using them.

I also run a low voltage cutout (Jaycar kit) which can be adjusted foir any voltage I like. I set it at about 11.9 volts. If it cuts in, the voltage at the battery is usually about 12.1 volts because the cutout is located near the fridge and there is a small voltage drop in the 8g wire to the fridge.

I use a cranking battery as my second battery and it lasts longer than any "deep cycle" I've used in the past, recharges more quickly and is relatively cheap to purchase. I have no reason to change from twin cranking batteries - I'm using the vehicle every day, so the cranking battery is always getting recharged, and the new engels are very economical on power.

Cheers
Phil