I think it is worth it but to determine if your batteries do need external charging, you can check your battery voltage with a multimeter with the engine off. If the voltage is 13.2 to 12.7 it has "surface charge" and this doesn't reflect battery health, but it does mean that your battery is fully charged.

If the battery voltage is 12.6-12.5 it's essentially fully charged and I wouldn't bother charging it.

If the battery is 12.4 or below I would charge it - it's not something you need to obsess about but 12.4 is not a fully charged 12v lead acid battery.

Chronic undercharged batteries deteriorate faster, including making them more resistant to recharge as well as reduced capacity when fully charged.

Noco and CTEK are popular smart chargers and the one I would recommend is the CTEK (56-353) MULTI US 7002

 

i think CTEK (40-255) is now sold as subaru accessories

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I would say if the vehicle is driven regularly it should not need external charging. If it sits undriven for extended periods of time then it may be worth putting a trickle charger on it.

I have a Miata that only driven during the warm months and I'll put a battery tender on it over the winter or anytime it sits for for more than 2 weeks undriven.

The key is not to let the battery run down completely. These batteries are not designed to "deep cycle". If the battery fails on a regularly driven vehicle then it was probably just not a very good battery and there probably wasn't much you could have done to extend it's life.

 

I use maintainers regularly and just about always have two going. Currently I have three maintainers in use. My plow truck never gets driven on the streets and the electric/hydraulic plow pump is very hard on batteries, so I plug that in to a maintainer every time I am done plowing snow. I also rotate that maintainer between my Outback and my 2010 GMC Sierra when either one of those isn't being driven for a while. I also keep my quad plugged in to a maintainer every time I shut it off. Right now I have a third maintainer plugged in to my '77 Caprice which is stored inside my garage for the winter. I don't leave that one plugged in all the time, just to occasionally make sure the battery stays topped off. Actually I just remembered a fourth maintainer I have going but it is at my shop, plugged in to my old '76 Craftsman garden tractor with the snowblower attachment on it.

 

Once a month placing your battery on a light charge over night is good for the battery while long distance driving is also good for the battery, short running is not as it only just tops the battery up. The modern car is draining the battery continuously so a charge on the charger will give the battery hopefully a longer life. Please be aware when placing your car on long term trickle charge check the trickle charge for heat and also the battery they can cause garage fires.

 

Commuting of 30 minutes each way 5 days a week, short trips to the grocery store on the weekends with the occasional 20 minute ride on the highway. My 2021 has been SOLID battery-wise. It IS garage-kept at home, parked outside at work. I've parked it for 5-7 days a couple times, it always started right up. Oh - I also have the headlights set to auto, I'm not actively turning them in an effort to trick the charging system.

 

I do not drive as regularly as you, but I too have found my 2021 Premium to be fine after 5-7 days of not driving. I do not use the auto headlights, but do turn them on near dusk (before the auto would turn them on) or in heavy traffic, and also turn them off when I stop the car. My car is a keyed ignition, so it is not awaiting a fob signal.

I also have been in the habit since pre-Subaru days of turning ALL accessories off when I stop. For the Subaru, that now includes turning the radio OFF (not just muting), turning the climate control and seats off, and having the cargo area lighting set to off. When I go into the cargo area, I just turn on the (now LED) light and turn it off before closing the hatch (hatch is manual, not powered.

 

The factory battery which was a Panasonic brand lasted the best part of 7 years l did give it a slow charge once a month or there about as it got older l think that prolonged it life. I don't expect that sort of time out of the current battery.

 

My OEM battery lasted a few years then I got a AAA replacement which only lasted a few months because there's a bad batch of batteries that came through current battery which the AAA replaced is doing fine I can listen to my radio for 10 minutes without running the car if you don't run your car everyday run it for 5 minutes a week and you'll be fine

 

5 minutes idle time once a week will not charge a battery. In fact, starting a car and running it for 5 minutes once a week may drain more energy from starting, than what can be replaced by charging for 5 minutes.

All of this may depend on the particulars of the battery's internal resistance/charge acceptance, initial charge, the car's charging algorithm (mine shows as low as 11.9 volts at idle - this is NOT charging the battery - it's draining it. but will jump to 14+ volts if I put the turn signals on.) That's the rub with today's charging systems. They do not behave in a way that one may expect based on old school systems that always ran a 14+ volts at idle.

 

Plus idling an engine for 5 minutes creates a ton of condensation inside the engine (and exhaust too), which creates acid, so not very smart. If you're not going to drive a vehicle for at least 10 miles in winter, leave it alone. Just charge the battery with a smart charger; that's what I do to extend the battery's life of all my vehicles.