Combine deep cycle marine battery with lawn mower battery in car

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Battery finally clicked its last click. After months of trouble with it it finally quit. Threw a nearly brand new Everstart U1R in as a temporary fix, and I have a Deep cycle one laying around that no one’s using yet. Any reason not to use it as a supplement for that poor lawn mower battery? Especially for basic tasks like running the blower fan for a few minutes while the car’s not running or rolling windows. I have old wiring ran for an amp I used to have, no reason not to just put the deep cycle onto those wires? I know I should just get a real car battery but money’s tight and I want to get by with what I have for maybe a month, if that
 
Short term, no problem at all. They are designed for longer, lower output draws rather than high amperage cranking. In colder weather this is more of an issue than in summer, as it might not have the CCA to start a car very well. I can give you multiple technical reasons not to do this, on the other hand I know of multiple anecdotes where people did it and the battery was fine, even long term. But a month? No problem regardless.
 
Batteries are strange. No idea how those two would run in parallel, but likely not a disaster, I'd try it.

As you've discovered, a healthy small battery will often work really well in a vehicle that typically uses a much larger battery. Race cars do it all the time.
 
Only $70 for a proper solution at WalMart.

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What car is this? I'd just run the marine battery as your primary and call it good. If the terminals hit the hood, cut 'em off. My marine batteries are "dual purpose", both for starting and deep cycling.
 
What car is this? I'd just run the marine battery as your primary and call it good. If the terminals hit the hood, cut 'em off. My marine batteries are "dual purpose", both for starting and deep cycling.
05 Chrysler minivan, the deep cycle admittedly isn’t mine so I don’t really want to ruin it by cranking 2-3x a day
 
Battery finally clicked its last click. After months of trouble with it it finally quit. Threw a nearly brand new Everstart U1R in as a temporary fix, and I have a Deep cycle one laying around that no one’s using yet. Any reason not to use it as a supplement for that poor lawn mower battery? Especially for basic tasks like running the blower fan for a few minutes while the car’s not running or rolling windows. I have old wiring ran for an amp I used to have, no reason not to just put the deep cycle onto those wires? I know I should just get a real car battery but money’s tight and I want to get by with what I have for maybe a month, if that
I would get that lawn mower battery out of there. If you have your mind set on parallel connecting batteries. they should be similiar ones.
 
Just don't get the cranking volts too low as to harm the starter. Volts go down, amps go up. High amp draw is not good for a starter. Your "probably" ok but, if engine doesn't spin over as if correct battery was installed I might do something to get right battery.
 
Just don't get the cranking volts too low as to harm the starter. Volts go down, amps go up. High amp draw is not good for a starter. Your "probably" ok but, if engine doesn't spin over as if correct battery was installed I might do something to get right battery.
Maybe I can send Google a bill like that one Lithuanian guy did
 
What kinda car? U1 will probably be ok with a 4 cylinder in the summer and will eat the brunt of the starting load, until it can’t. At least it’s not an expensive battery. Mazda uses smaller in some of their cars. It may quit without warning. Doubling up the U1 with the deep cycle might protect the U1 a little, but this seems janky to drive around with. Put one under the hood, and keep the other charged as a “jump pack” in the floorboard. OTOH, if the deep cycle is a mixed use, and it fits, I’d just run that.
 
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