Request for Advice: 3.5yrs 12V Battery Replacement Time?

I got caught up in the MPG issue and forgot about the OP. I would say the OPs battery has a problem being left to sit for long periods of time. Seems like if the car is going to be driven daily he can keep it and if he plans to let it sit again, he might want to replace it.

 

Please let it go on until it works. Given the voltage, you would probably have the record for the longest running original battery. 10 years would be awesome.

 

Looks like 10 years isn't going to happen. I just tested it:

 

ya, my 04 lasted until last spring. not too shabby. fortunately, it didn't die and mpg's never went down. it just started doing funny things like sks touch handle wouldn't work and you had to hit the fob. then after a few weeks, you had to put the fob in the slot. then one day, i needed a jump. but i knew that was coming and was prepared. i think the older batteries were built better.

 

so just for grins, and while the Prius is home for the weekend, I went out this morning and hooked up the charger at the jump start terminal under the hood. It was 12v+ on a voltmeter before connecting and the charger immediatly pumped in 6amps @ 15V. Within 5 minutes it had dropped below 2amps. That is what I would expect for a healthy battery.

 

Be careful when using that battery charger on the Prius battery as it should not be charged at a rate higher than 4 amps (directions on the battery and in the handbook). As this can cause it to gas to much and release pressure through the safety vents, and overheat. This dries the battery out causing it to fail. I am sure for the length of time you had it on charge no damage will have been done, but if left unattended for a few hours could easily do so.

 

I use battery tender brand and it has been working fine for about a year (charging once a week roughly). I have also heard good things about a product called battery minder. It seems that can de-sulfate your battery to improve its life. Have never used it though.

I like the slow charging one but there is also a 1.25A version. One drawback is that I have to open the hood to connect it every time. It has ring terminals but unfortunately, they are not long enough to come out in front of the hood. That would have made connecting the charger really easy.

Battery Tender 021-0123 Battery Tender Junior 12V Battery Charger : Amazon.com : Automotive

BatteryMINDer Model 12117: 12 Volt 1.33 Amp (12V 1.33A) Charger/Maintainer/Desulfator : Amazon.com : Automotive

 

Sorry I cannot recommend a charger as I am in the UK but I would look for a charger that is suitable for AGM batteries and has an output of around 2 amps or is switchable to this. An automatic 3 stage charger would be best but a simple 2amp charger would be fine just left on over night.

 

I replaced the OEM battery with an Optima YellowTop about a month ago. OptimaJim has indicated 10A is fine for this battery, but the warning is appreciated.