2021 Prius. My 12V battery is starting to drop in voltage more than I'd like after the car is parked for a couple of days. I am considering replacing with AGM (Yuasa brand). I understand AGM has a slightly higher terminal voltage and a lower internal resistance (allowing faster charging on short journey). Sounds good. However are there any downsides to switching to AGM other than higher price?
Other than the charging algorithms are slightly different for the two types (and thus the AGM wouldn’t be receiving the correct charge) nothing that I’ve heard of. They are close enough you probably wouldn’t see anything, but for the Gen 4 not sure what benefits you would gain.
If you decide to get one, make sure it is designed for high heat. Even the heat tolerant versions may ultimately rely on some sort of aftermarket insulation and forced air cooling. Previous Prius generations relied on an AGM battery for that rapid recharge capability, and they were placed far from the ICE in the right rear corner of the car. AGM is more expensive also, making a premature failure due to heat a cost consideration. I have a separate beef with the replacement Toyota TrueStart battery. My OEM battery from the factory had removable cell caps so a person could keep the electrolyte topped up. The desert heat and aridity here will be pretty rough on this so-called maintenance-free battery replacement. Hope mine holds up.
