Hello.

The battery in my 20 T4R with 35k on it seem to be dying, and it is a bit surprising. This may be a poor practice, but I have headlights on all the time and let the car turn them off automatically. I also have an in-cabin dual battery that I have used occasionally, sometimes for longer period of time and sometimes just for a few hours. I use a RedArc DC-DC1225D for control of charging and I know it doesn’t charge if the engine is not running - I have it wired to the ignition fuse so it knows when to charge.

Could any of the above be the cause of the battery’s seemingly shorter life? I have extended warranty on my car although I don’t know if it covers the batter. How can I find out the power rating of the alternator? It could be that the alternator never is able to charge two batteries when the second battery is inline?

What do you recommend in terms of a better battery to replace the main battery with?

Thanks in advance

Farzad

UPDATE: my T4R has been basically idle since beginning of 2023 when I purchased a Prius to save on gas when in town or when the T4R is not needed. Since then I may have started the engine a few times. This by itself could be the cause of battery losing its capacity, but I have also learned that I need to check the alternator and make sure it is delivering the power that is needed.

I'm jaded since Arizona eats batteries, but depending on the "in-service" date of your vehicle, I wouldn't be overly surprised to see a battery failure in 3 to 4 years. I've been thinking about replacing the one in my 2020 Pro (44K miles, purchased in November 2019) pre-emptively to save the inevitable dead battery that I know is coming (probably on a nice 115 degree day this summer).

The initial battery in my last few vehicles (VW Golf R, Land Rover Disco Sport, Jeep Wrangler) all failed within 3 to 4 years.

In some cases batteries are warrantied for at least 3 years from the manufacturer. I know my Rover got a new battery for free after failure in less than 3 years. VW only warrantied for 2 years though which was ridiculous (factory battery failed in just over 2 years). Extended warranty typically will not cover it.

Thank you for the note. I bought my 2020 T4R sometime at the very beginning of 2020, so the in-service is straightforward.

One thing I forgot to mention, and I will see about updating my original post, is that since beginning of 2023 I have rarely used the T4R because I have bought a new Prius for point-A-to-point-B travel and I think when the car is sitting idle for a few months the battery could get discharged. There are a few tests that can run to see if the alternator is doing its job of delivering sufficient voltage and current.

I'd say you hit the nail on the head by leaving it idle for months on end. I'd replace the battery and start using a battery tender if you know you aren't going to drive it for awhile. 3-4 years is on the shorter end, but not unheard of. Mine is a 2018 and I just bought a new battery just in case. The factory one seems to be having a harder time starting, but it could be the colder starts in the winter even in the garage (it usually stays around 40 degrees). Regardless, 5+ years is getting my monies worth. Small price to pay for having a dead battery with two small kids in the dead of summer somewhere.

Yes, modern cars use electricity while the car is off. The newer, the worst it gets. At a minimum, the electronics are on, waiting for you to press the unlock key on your key fob. The latest Toyotas have a DCM (data communications module) that is always on, and "calls" Toyota periodically to update the car status (tire pressure, fuel level, location, etc). All those will discharge the battery over a period of time. The longer the car is off, the more likely the battery will discharge. (You can see your car's status in the Toyota app on a smart phone).

Is your last sentence a question or a statement? Easiest check for the alternator is to measure the battery voltage while the engine is running. It should be 14 to 14.5 volts. If outside that range, something is wrong.

The alternator will put out what ever current is required. The 4Runner has a relatively high capacity alternator, so you need not worry about the current unless you have something that takes a lot of current (example a winch).

If you leave your car parked for extended periods, suggest you get a battery maintainer (NOT a trickle charger). That will keep the battery charged even though the electronics are using some current.

Definitely could have contributed. From what I've experienced personally, a battery that is starting to get weak can definitely start to have more issues if you do not use the car. The Rover battery we had fail started to act up after the car was parked for 28 days during a long summer vacation (while we were driving the 4Runner).

You can always drive the vehicle once every couple of weeks also to try to keep the battery in a better state of charge if you continue to have issues.