12-v. battery died

Most cars with alternators will charge the batteries at 50/60amps for a short period to bring the battery close to full charge in a short period of time. The Prius only charges maximum 4amps and so requires a much longer run time to recover from a partial discharge and it does not matter what battery is fitted be it OEM Optima or lithium if the charge time is not long enough it will end up flat.

 

this happened to daniel? aren't you a little seasoned to be getting dead 12v batteries? (hehe.. j/k)

there is a way to release the hatch from the inside. it's simply a PITA. you have to crawl back and get everything out of your way... lift up the bottom floor.. if you're good you can remove it... there is a access plate in the rear center of the tray on the back wall. pop that out. reach in with your palm facing the bumper and press up on the softer round piece... if you'll do it right, you'll hear the hatch lever rotate... push up on the hatch with your shoulders. if you don't life the hatch high enough at this point, it will lock back down (kinda odd to do when your hand is holding the latch.. uh... connection rod piece.. thing... it's odd)

 

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And if you have a smart charger, like we do on our boat, the charging will be done in stages: Bulk stage, Absorption stage, and Float stage.

Bulk stage is limited only by the ability of the charging system to produce power. For our boat, this is 100 amps from the alternator or 100 amps from shore power. Full amperage is delivered until the surface of the battery plates saturate, causing the battery voltage to rise, triggering a transition to the absorption stage.

Absorption charging is done at a constant voltage. During this stage the recharging reaction works its way deeper into the battery plates. The deeper it goes, the slower the battery can absorb charge, causing the charging current to trail off toward zero as the battery approaches a full charge. When the current reaches a low threshold, the battery is considered fully charged (or close enough), causing a transition to float.

The float stage holds the battery at a fully charged state. The charging voltage is high enough to compensate for self discharge, but not high enough to overcharge. This stage is held indefinitely, or until the battery is used and needs to be recharged.

With the Prius, all battery recharging is essentially done through float charging. This is not a very quick or effective way of recharging.

Tom

 

That's interesting Tom. One question I'd like to know. What is the approximate per cell constant voltage (or per battery voltage) in the absorption phase?

Thanks.

 

It depends on the battery chemistry, but for a 12v AGM lead acid battery the absorption voltage is normally around 14.9 volts. Here is the chart from a typical charger:



I didn't mention equalization in my previous description because it is not used for all batteries and normally it is only used periodically to condition a battery. Equalization is used to control the build-up of lead sulfate.

Tom