oct 2012 Truestart battery

Has the battery been fully or well discharged, and then recharged by the Prius. The OEM battery has a maximum charge current limit of 4.5 amps, and the Prius can recharge it at more than 10 times this limit. It is my belief that this dries the battery out, and causes it's early demise.
The charger must also be suitable for AGM batteries a flooded lead acid battery charger will likely under charge it.

John (Britprius)

 

I edited and added a line to my post about chargers did you read that.

John (Britprius)

 

This "may" be the problem. AGM batteries require a higher charging voltage than standard car lead acid batteries. The charger needs to have a voltage output of 14.2 to 14.3 volts to get the battery at full charge.

John (Britprius)

 

The Prius charging system is quite good at keeping the battery topped up if the car is used on a regular basis. But the battery is rather a week link.
I use a 62 Ah mobility battery that fits snugly in the OEM position. These batteries are truly deep discharge batteries, and will put up with lots of abuse at a price well below the OEM.

John (Britprius)

 

JC, As John (britprius) stated above the charger you have doesn't sound like it is designed for AGM type batteries.

I too have one of the "True Start" brand batteries from Toyota. It is now 12 months and ten days old. I keep it charged up with a smart charger set a 4 amps on the AGM setting and have no problems getting the battery up to 12.9 on the MFD and 13.1 with a digital VOM at the posts.

I would suggest you look into getting a newer smart charger than has the AGM settings on it. I use the Battery Minder 12248 and it works great for me. Others on this board recommend the CTEK brand of chargers. Those too also offer the AGM settings. As mentioned, the parameters for charging a AGM type battery are not the same as a standard flooded battery. The voltage cutoff is much lower on the flooded type versus the AGM setting. Also if you continue to charge the battery with a standard charger, you will shorten the life span of the AGM battery as you are not "fully" charging the battery.

BatteryMINDer Battery Charger / Maintainer with Desulfator — 12 Volt 2/4/8 Amp, Model# 12248 | Battery Maintainers| Northern Tool + Equipment

CTEK Multi US 4.3 - CTEK Battery Chargers

Hope this info helps!

Ron

 

If you have a northern tool store close to you, go buy one of those Battery Minders. I had a 30 day return option on the one I bought. I bought it two years ago when the old OEM battery was getting weak. That should tell you how much I like it and that it does the job. I would have taken it back if it did not work as I paid around $130 for it. I am a poor man on disability so I don't tend to throw my money away. I think you will be pleased with your investment.

 

$130...yikes....I was thinking about replacing our charger -- but it still works perfectly, just not AGM -- as I remember, paid about $50 for it five or six years ago.

This is the one I now have and as far as I can tell, would not want to use it on the Prius battery....Battery Charger, 12V (SE1250 ) at Aubuchon Hardware

 

It's better than not using a charger at all.

 

I would not hesitate to use it if I needed a charge. Just need to understand that it might not "fully" charge your battery. That does not mean it won't charge it up enough to get the Prius in ready mode if you happened to run down your battery.

 

You are not the first person to be caught out by the charging requirements of AGM batteries nor will you be the last. The difference is not easy to understand, but as stated previously the voltage for AGM batteries needs to be at leased 14.2 volts. Charging with some flooded lead acid chargers results in under charging and possible battery damage from sulphation if left in that state.

John (Britprius)

 

Since I have several DC lab power supplies around, my idea of a 12V AGM charger is to set a power supply with 3A output to a voltage output to 14.4V. The result is constant current charging until the current drops below 3A; then constant voltage charging at 14.4V beyond that. I find that a Prius AGM battery in good condition will be charged up when the current flow drops down to around 60 mA or so. If the current flow remains substantially higher, that is a clue that the battery is showing signs of deterioration, but it can still be kept in service.