Starting Or Deep Cycle Battery?
 

Suppose you have a car that is not driven for significant periods, not meaning long term storage but let's say the car sits idle for three weeks to three months at a time. Long enough for the battery to sometimes go flat. Would it make sense to install a deep cycle battery, so that repeatedly going flat doesn't mean buying a new battery? Can deep cycle batteries be used as starting batteries with no problems?

Yes, but they take longer to charge. So, firing up the car for a few minutes every week ain't gonna do it. Why not get a battery-tender?

Optima red-top paired with a C-Tech charger.

I think I killed my second Optima in 2 years by not driving the car enough. I think will buy the C-Tech charger if that really does the trick.

Is the trickle charger the only way to keep an Optima battery alive if you don't drive your car enough?

I use a battery tender (the "smart" kind that does not overcharge) on my Buick, which gets parked from October to April... works great.

Battery tender. I have them for the 930 and both bikes. On the 930 the little plug hangs out the front spoiler for easy connnection.

Yeah, wouldn't one of those smart trickle chargers be a better answer?

A trickle charger would clearly be the best thing to do, but my garage is miniscule, will hold a 911 and a thimble but not both. Sometimes the 911 ends up parked on the street for a week, which stretches to two, and three, and . . . shouldn't happen but it does. I am experimenting with a solar trickle charger now.

I certainly do not know how the internals (guts) differ on a standard battery vs deep cycle. But the ONLY application I was aware of for a 'deep cycle' battery is for trolling motors and lighting in boats?

My though has always been they are designed for low amperage draw over LONG periods of time, (slow draw-down).

In fact most fishing boats have deep cycle batteries for just such applications, and a standard battery for starting the engine ...don't they?

I don't think they are designed (internals) for large, instant current draws.

...but I may be wrong.

Dont you own an extension cord?

I've been using the Optima Blue tops on my bass boat for a long time. I've got a humongous blue top as my primary trolling battery, and a very old (but still good) smaller blue top as a second trolling battery (for 24V turbo trolling). When my boat cranking battery died a few years ago (I'd always used "regular" batterys for that one), I purchased a smaller Optima Blue top "dual purpose" deep cycle and cranking battery and it seems like it might be perfect for a 911. I might be wrong, but I always thought trolling batteries could be depleted (I know I have many times), but it was important to charge them back at the end of the day (I always have). I now keep Battery Tenders on them so I never let them discharge and sit for long periods of time.