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I bought a 2010 Golf in march and I do not know how old the battery is (no dates on the battery) and with winter coming in I feel a bit nervous.

Usage
I do not use the car very often but I try to give it a 30min ride once a week.
The car is parked outside on the street, no garage or access to power socket to charge the battery.

Measurements
Before driving, the battery will typically show 12-12.15V and the car starts even at -5°C. After driving 40min the battery shows 12.7-12.75V. Measures were made with the battery connected and car locked to minimize load. A few days after driving the battery will be back to ~12.1V.

Is my car battery health OK or is it close to end-of-life?

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    Personally, I wouldn't replace it yet but it depends on how important 'peace of mind' is to you. Assuming you don't park on the street and you have 110VAC in your garage, have you considered a trickle charger or even a battery warmer? Looking past voltages and assuming a battery that isn't sealed, what does a hydrometer say? Are there dead cells? Have you unhooked the negative terminal and used a VOHM to measure parasitic power drain? – user16128 Dec 5 '19 at 7:19
  • @Jeeped thank you for you comment, I realized I forgot to mention that the car is sleeping outsite (no access to garage or power outlet). I edited my question. Peace of mind important and tow-service x1.5 the price of a new battery where I live. – Thibault D. Dec 5 '19 at 8:04
  • (Answer to your questions in order: Not available / Not sure how to do that / Don't know / Haven't tested that yet but should give it a try) – Thibault D. Dec 5 '19 at 8:06
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I think your battery is okay. You are getting 12.7 volts after driving, which means that it is fully charged. It's the charge after sitting a few days that concerns me, 12.2 volts is generally considered 50% charge, 12.0 is 25% charge, so after a few days your battery is dropping below 50% charge. That's actually fairly normal as modern cars have battery drains from alarms and other devices that stay on even when the car is off.

One thing to check is the battery capacity, and make sure it's sufficient for your car. Sometimes people skimp on this and get a battery below the recommended capacity or on the low end. A lower capacity battery will drop more when sitting under typical standing loads. The capacity should be written on the battery somewhere. If it is low for your car then I would replace it with the highest capacity battery you can fit in the car, this will have a higher charge after sitting a few days.

I would also do a battery drain check on your car using the ammeter function of your multimeter. If you are getting more than 100 milliamps drain (as measured 30 minutes after you turn the car off) then you have a high drain and need to get it looked at. If you are getting close to 100 then see what you can do to reduce that.

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  • Thank you for you answer and tips. Capacity is 62 or 65Ah which seems rather standard. To do the drain test, you disconnect one of the battery connectors and let the current go through the multimeter, is that right? ("Car -> Battery pole" to "Car -> Multimeter -> Battery pole") – Thibault D. Dec 5 '19 at 11:45
  • That's the right process, just make darn sure the ignition is off and stays off or you'll blow the fuse on your muttimeter. Also, it takes awhile for modern cars to completely sleep, you need to wait a good 20 minutes sometimes for the drain to drop to its lowest level. – GdD Dec 5 '19 at 11:54
  • Also, if the radio has an unlock code, you will probably need to re-enter it after having the battery disconnected. – thomasa88 Dec 5 '19 at 18:55
  • @GdD I did the drain test and I get about 5milliamps :o – Thibault D. Dec 6 '19 at 13:28
  • That's actually very low @ThibaultD. , good news. – GdD Dec 6 '19 at 13:30

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