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I have an older car (2006 Volvo XC90) which I drive occasionally (once a month). I am planning to buy a new battery for it. Ideally, I would want a battery that can handle being charged only once a month, and the temperature swings that can happen over a month. I'd rather not blindly spend a thousand dollars for the best battery on the market unless it's actually necessary, though.

What should I look for in my new battery?

  • Is there a type of battery that works particularly well in this situation? These days, it seems like there are new battery technologies like gels, dry cells and lithium-ion batteries. Would any of these drain less over long times/temperature changes?
  • What specs (such as CCA or Ah/capacity) are worth paying more for? My manual recommends 600 CCA and "120 min reserve capacity".
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    If you are worried about the battery staying good, get a battery tender you can plug in ... it will keep the battery fully charged and ready to go. And with it fully topped off all the time, the battery should last longer as well, without the need to worry. Commented Nov 6, 2022 at 18:46
  • I agree with Paulster2, a battery tender would be the best choice but you could use a deep cycle battery that may hold a charge for a longer period of time.
    – X-tech2
    Commented Nov 7, 2022 at 3:52
  • If you drive the car occasionally, once a month, just remove the negative lead for the period you don't drive it. This will not drain the battery (when it's not too cold). I'm not sure how healthy is the regime for the car (driving it once a month)... Digressing a bit, if you only drive it once a month, why do you need it? Commented Nov 7, 2022 at 22:26

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Buying a float charger would be the best way to ensure you don't repeatedly damage batteries, but it could be the case that 1 month of staying unused might be not too long, assuming when you do drive the car, it's a good long drive (or several drives) and not something like 30 minutes and then 1 month of parking again.

Lead-acid batteries do self-discharge, and cars also have parasitic loads. What the parasitic load is, varies from car to car. For example, my car (Toyota RAV4 hybrid) has a keyless entry system. The keyless entry system all the time transmits ping signals to the key, to get a response. The problem is, those constant pings slowly deplete the battery.

Thus, there is a battery saving scheme:

  • If the smart key system hasn't been used for 5 days or longer, its response time becomes very slow. So it will take a lot of time to unlock the doors, and it's not as instant as it usually is.
  • If the smart key system hasn't been used in 14 days or longer, only driver's door works for unlocking and not the passenger's door

If your car has a smart key system without such a battery saving scheme, it's plausible that in one month, the 12V battery could be flat, or if not completely flat so deeply discharged that the deep discharge might have shortened its lifetime.

As for battery specs, there really aren't much to choose. Your car most likely has a certain size battery holder, and that limits what capacity you can buy. Bigger capacity would of course handle longer parasitic draws, but that's impossible given the limited space. So the only choice you may be able to do is by different types of battery (flooded vs AGM); AGM doesn't dislike deep discharge as much as flooded, but it still isn't a good idea to deeply discharge AGM.

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  • This answer covers all the grounds. The OP is asking for the Impossible. No battery which fits in the OEM box can run for a month on non usage on a XC90, it had a lot of electronic modules and they all eat up a hefty battery percentage. What the op can do is daily start the suv and move it around a few feet forward and backwards for 10 minutes. This would ensure the oil is circulating, and lubricating where necessary, and the minor breaking will ensure the pads not getting stuck to the rotors as well as keeping the tire sidewall intact. Every car collector follows a similar routine. Commented Apr 1 at 0:40
  • And since you drive very less, your car fluids would have to be change frequently. For this type of usage, engine oil should be changed every 6 months. And each year I would also change the remaining other fluids. Your usage is very less so chances of buildup of unwanted substances is high. Even if you buy an electric car lubricating greases and fluids would need to be changed with such a less driving frequency. And they batteries would require more maintenance per cell basis. Commented Apr 1 at 0:43

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