Car Battery left sitting over winter, wont hold a charge

Question

2009 toyota matrix has not been driven regularly since 2019 when it got a new battery. Since then we have removed the battery and stored it indoors (not on a trickle charger) for winter then in the summer installed it in the car which we will drive 5-10km a month in to spin up the alternator. In May I installed a new radio in it as I was planning on insuring the car and driving it which did not end up happening. Now the battery will lose charge within week or 2. My dad thinks it is the new radio since the battery has little to no use. I tried to explain that since it was not on a trickle charger and it is not a deep cycle battery that we likely killed it by letting it sit to over 2 winters. Any thoughts? I am insuring the car in a week for work and don't want to get stuck:)

Car Radio for reference: https://www.amazon.ca/dp/B07Z4KY6X1/ref=emc_b_5_t

Answer 1

I would agree with jwh20's assessment, but would add to it, more to your question.

You've actually done more to keep your battery straight than most people would. I really don't think the battery is dead if it's staying charged for two-ish weeks. I'd definitely think there's some sort of drain happening to it, and with the radio being installed recently, it's a likely culprit. The easiest way to tell if this is what's causing the problem is to pull the fuse to the radio and see if the battery keeps up.

You can check the amperage draw on the system by using a multi-meter with the built in amperage function. Disconnect the battery and put the multimeter leads between the two points. This should give you the amperage draw. Then pull the radio fuse (if you are using the original power wiring of the radio to power the new head unit) to see if there is any change. At this point there may not be a change in the draw and it still might be the radio. It might do this if it is wired incorrectly and is pulling power directly from the battery or if it is going through a different circuit to pull power. If the power draw doesn't change, then you'll need to check them one by one reading the multimeter at ever step to find the draw.

Something else I'd take a look at is if there is a built in amp in the car which is being powered all the time. If so, it would drain the system over a short period of time, like you're talking about.

Answer 2

First, take the battery to a shop that services batteries and have them load test it. If it passes, chances are that it's OK and just needs to be fully charged or you have a drain on it and you need to find and correct it.

If it fails, get a new battery and, after fully charging it, install it in the vehicle. You may still have a drain but you'll want to find that with an ammeter.