Part Time AGM Battery Maintainer

Almot wrote:
Though I doubt there is ay place in the US that can be that hot for that long.

Phoenix, AZ averages 90+ days a year over 100F. I would imagine that most of the southwestern, low desert areas do also.

When it's not in use camping, our Optima Blue-Top is plugged in to a WalMart Schumacher float charger, under $20.00. Six years of year-round camping trips and very happy - would NEVER go back to weat lead-acid batteries, just too many advantages for our application with an AGM.

It's certainly not necessary to have a continuous charge on the AGM. As others have mentioned, self discharge rate is very low.
I've had an AGM outside on a shelf for over 6 months and, when returned to service, it had almost full charge.

Almot wrote:
My manual says that drop below 60% may result in irreversible loss of capacity.

A month or two with loads disconnected should not be a problem for AGM. Just make sure you do disconnect them - no fridge running, no radio on standby, nothing. At 68F AGM have very low self-discharge current, typically 3% of initial charge a month. When it's really hot, like 104F day and night, 24/7, then self discharge increases to 10-12% a month so it will take 2 months to drop to 75% - still no need to maintain. Though I doubt there is ay place in the US that can be that hot for that long.

Interesting! Whom is the manufacturer and what model?

My manual says that drop below 60% may result in irreversible loss of capacity.

A month or two with loads disconnected should not be a problem for AGM. Just make sure you do disconnect them - no fridge running, no radio on standby, nothing. At 68F AGM have very low self-discharge current, typically 3% of initial charge a month. When it's really hot, like 104F day and night, 24/7, then self discharge increases to 10-12% a month so it will take 2 months to drop to 75% - still no need to maintain. Though I doubt there is ay place in the US that can be that hot for that long.

Most AGM batteries only loose 1-2% of their charge per month while in storage, unlike wet cells that can loose as much as 20%. There is no need for a maintainer if the battery is fully charged when put in storage and an ocasional check on the state of charge, not allowing it to drop below 50%.
Allowing any battery to drop below 50% state of charge is inviting sulfation. Much better/easier to prevent it than deal with the result.

DougE wrote:
Is it really necessary to run the CTEK 24 hours a day? It would be a simple thing to put the maintainer on a timer and just run it a couple of hours a day.

Depends on how smart the Ctek is. If it backs off when the batts are charged, set it and forget it.