# Prius 12V auxilliary battery replacement



## Ziggythewiz (May 16, 2010)

FLA and SLA have different charging profiles, so an SLA could easily be damaged by a charge system designed for FLA.


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## samwichse (Jan 28, 2012)

Have you considered a motorcycle or lawn mower battery? A lot of the g1 Honda insight guys buy a $25 lawn mower battery and it works just fine.


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## Moltenmetal (Mar 20, 2014)

The "charging system" in this case is a simple DC/DC converter, presumably operating at constant voltage, rather than a dedicated charger- akin to an alternator in an IC engine car. So are we talking about a real difference in operating life between SLA and flooded lead-acid, or a theoretical one? 

The SLA's data sheet asks for 14V (ie. 2.33 V/cell) with an initial charge current limit to 0.1C. Assuming the battery is not allowed to run flat between charges (i.e. assuming I can get my daughter to NOT turn on the dome light and leave it on), is there any real difference? Note that the FLA battery is buried in the trunk, so in the 7 years I've owned it I haven't added any water etc.


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## Moltenmetal (Mar 20, 2014)

I know of at least one guy with a lawn tractor battery in his Prius which is working fine, so I guess that is my fallback. Definitely not dropping $209 plus tax on this stupid thing.


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## Moltenmetal (Mar 20, 2014)

Begs the question though: the original plan was to just parallel the aux battery with the output of my DC/DC converter on my EV conversion. The SLA size U1 was CanEV's recommendation and that's all he does with them- no other charging circuit, current limiting resistor etc. if it will work in the EV without destroying the SLA battery prematurely, why wouldn't it work on the Prius?


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