OEM battery lasts very long so how to tell if it's weak?
 

I'm used to my other vehicles' batteries hardly lasting more than 3 years, so I would actually change it around the 4 year mark automatically to avoid getting stranded. Those batteries were cheap anyway and I could replace it myself after buying from Autozone or Advance Auto Parts and not much else to do after changing it, electronics-wise.

But the Audi battery looks like it's an expensive replacement and not something I can do myself, due to all the electric resetting junk. I have a 2018 Q5 that's a CPO, and I'm assuming it's the original battery. I've seen some people post on here that their battery lasted like 7-8 years. How do I tell if the battery is going bad? I notice some slow cranking but it's also cold mornings here in NC - I already forgot what last winter was like. How about checking the battery voltage somehow? I'm not used to AGM batteries and how long they last or how to test them.

I do carry one of those lithium-battery packs with jumper cables from Amazon if I do get stranded, hoping it has enough juice to turn the starter over.

Any battery can be tested for its health. I believe most autozone stores can test it.

AGM in a normal car is likely to last a lot longer than AGM in a stop/start car as well, depending on how much you exercise that stop/start. But yeah, the normal thing is to load test it, being sure that the tester is AGM aware as the discharge profile of an AGM vs a basic wet flood is not the same.

But you can also look at the info in the measuring values of the J533, same module where you update the adaptation values after replacing a battery. But that would require having a relevant tool for the task, such as VCDS.

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Audi designs reasonable battery management systems and so is better than some other cars at shutting down parasitic loads and protecting the battery when parked. This attempts to save enough charge to restart the car. What is most likely to strand you is if the battery finally gets to the point where one or more cells fails and it can't deliver the right voltage, much less have enough cranking amps. If you're trying to optimize costs, I'd say you're on the right track. I am doing similar with my low miles 2017 Q3.

The main risk we're both taking is that if the battery fails and we jump-start it, we're be putting more strain on the alternator and charge systems. I'm not doing this to squeeze a few more weeks out of a battery, but because it seems right now that it could potentially last another year or more.

Really, I only carry the portable jump-stater if going far and/or overnight. Locally, I expect I'm more likely to detect a problem starting it at home (after a long park) than restarting in the middle of an outing, and worst case I can get roadside assistance or get home to grab the tool. I don't feel that comfortable having the lithium pack sitting in the cargo area all the time in all parking conditions.

If it does show a battery/charge system warning on the dash, or if you notice any strange electronics "glitches", I'd consider that a more significant sign that it is time to replace. A more gentle sign might be if you find the remote unlocking disabled, suggesting it has gone into an even deeper battery protection sleep due to low voltage.

Yeah, might just pick one of these up on Amazon - they are anywhere from $25-35 and have pretty good reviews for us occasional users on figuring out battery health and alternator issues.

Keep in mind that the alternator is LIN bus managed by the J533, so to really have a clear view on what's going on with the charging system, you have to have a scan tool that can interact with the J533. VCDS, etc. But a load test tool for the battery is always good. And at that price, .... I have my Optima 400 charger, and it tests for faults but not really for capacity.

Another tale tell sign is the start-stop function engages far less frequently (for those who prefer this feature). Before battery replaced after 5 years and 65k miles, S/S hardly ever kicked in. Afterwards, it was back close to the high frequency of my new Q5 (bearing in mind that several other conditions factor into the frequency of S/S).

I have a 2018 with a 2017 build date and 93,000 miles still on the factory battery.

just drive it until it dies. You can use a battery tester but they are not super accurate unless you are doing a true load test on the battery and the hassle of disconnecting the battery from the car and throwing a bunch of fault codes is not worth the trouble(these cars get grumpy when they lose all power).
Do not test the battery while it’s still attached to the car!
better to spend your on a jump pack should the battery suddenly die

I’ve owned several VW’s and Audi’s and never had a factory battery fail before 7 years old

2018 Q5 CPO... 4 years. The audi app let me know that the battery was going downhill with its monitoring voltage trend. So the Audi dealer says it was bad. 425 replaced and programed>

as mentioned. autozone or other auto parts store or battery stores fora test
good info on the S/S