For the past two weeks the only use our 2015 Prius has had is to drive it out of the garage a few times to make room for work of various kinds, and then to drive it back in again. I therefore thought it would be a good idea to give the 12V battery a top-up and connected my 2/10/15A "smart" charger. Initial voltage check showed 11.7V, so it seemed that a top-up definitely wouldn't go amiss. It's now been charging on the 2A setting (but actually showing 2.2A) for 6 hours or more. At the 3-hour mark the voltage was 12.5, after 5 hours it was 13.8V (which I had always understood was the normal voltage for a battery that was fully charged and on charge -- which is why so much mobile communications equipment is designed for that voltage rather than for 12V); now, at 6+ hours it's showing 14.4V, and the charger has still not switched to Float Charge mode. Should I let it continue charging, or is it time to disconnect the charger? BTW, this car was not sold until 6 months or more after manufacture, so is it possible that the battery deteriorated in that time, and its life has been reduced significantly? Addendum: I used the same charger on another vehicle yesterday (with a wet-cell battery), and the charger switched to Float Charge mode after a couple of hours.
Assuming the charger is set for an AGM battery, I think it'll switch to float mode pretty soon now. At five years, the battery is getting a little long in the tooth, but they last longer up in Michigan than down here in the armpit of North America.
6 months sitting at the dealership, particularly a negligent dealership where that's ALL it did, likely did reduce it's viability. Probably time to swap. Ours spend more time hooked up to a CTEK 4.3 than not, especially the last 2~3 weeks with COVID 19. I just hook it up, and leave it on. It charges, then switches to some sort of float mode, which can be indefinite, till you next need the car.
AFAIK "AGM Mode" is no big deal. You can charge in regular mode, especially if that's all your charger has. Stand corrected if wrong, but I believe AGM mode is just a slightly higher voltage, at least that's how it's described with my CTEK. Also, with my CTEK, that mode is recommended ONLY for AGM's with the spiral style innards (aka 6-pack). The AGM Mode is NOT recommended for AGM's in conventional case. Maybe just with my charger, not sure. Check with the charger manual.
I did see the voltage up to 15.0 with the current starting to drop, and it did finally show Float Mode with the current at 0.9A and the voltage at 14.1. What would have happened, I wonder, if I had powered the car ON immediately after disconnecting the charger when the voltage was at 15.0? Would the various light bulbs have survived?
I agree, the system is designed with 15.0 V as a maximum. It’s part of checking the DC-DC converter is working properly, should be in the range 13.0 V - 15.0 V if I remember correctly. I have often started a vehicle while connected to a charger and then disconnect the charger afterwards.
It should do that regardless of what the setting is.......or if it has no selectable setting. If it does NOT, then it's time to shop for a new battery. The amount of time it is taking to get there might not be good but it WAS pretty low to start with.
