Prius dead battery - advice

[GreenV8S]

Artsy said:

Stopped it earlier and the battery is up to 10v from the 6.4 it was showing earlier sonim hoping something is happening.

You're wasting your time. A 12V lead-acid battery taken down to 6.4V is dead and won't be recovered by anything short of melting down the plates and.recasting them.

Some specialist lead acid batteries are designed for deep discharge, but a wet or AGM lead acid battery taken below 12V is going to be damaged. The voltage typically drops in multiple of 2V as each cell in term dies and shorts out. You can sometimes burn through the short circuit and get it to take some charge, but by this point the plates are so damaged that it'll have vastly reduced capacity, and it's pretty common for some cells to refuse to take a charge at all after they've been discharged that far.

[Artsy]

I guess I'll find out tomorrow

[tr7v8]

Mine is a Mitsubishi Outlander PHEV but sounds very similar. Yes you can jump it & the main battery will recharge it, But as others have said it won't recover and will let you down. All it does is start the engine and initialise the electronics. The big battery does everything else. If its the same as the Outy its a special battery is because it is in the passenger compartment and is fitted with a vent pipe. If you're an AA member then call them as they'll A. get it started B. test the battery to see if it will come back to life & C. if not flog you one & fit it at a competitive rate. It might be worth looking at Breakdown Repair Cover from the AA as that would have paid for a battery less excess. The last one they sold me was a reasonable price.

[Artsy]

I should add that the battery was still operating a couple of interior lights albeit very dimly so I'll at least give the recharge a go and hope.

If not, I at least know what I have to do in terms of replacement.

[5s Alive]

The original gen 3 Prius 12v battery is a flat plate AGM and was prone to failure. I changed mine at 3yrs for a spiral wound Optima yellow top from Tayna, it's a direct replacement and more robust than the original and it's particularly resistant to vibration, not that there's much of that on our billiard table smooth roads.

Toyota managed to leave my Optima at 2.8v after their woeful attempt at the Takata air bag recall. I didn't hold out much hope but charged it over 24hrs on a Ctek charger and it was still going strong when I traded the car 8 years later.

I wouldnt hold out much hope that your original 12v would shrug off the same abuse. I still have mine in the garage for other purposes but it doesn't get near to a full capacity charge no matter how long it's connected for.

[Alickadoo]

paintman said:

Alickadoo said:

Well, if you are a member of the AA and it is going to cost you nothing to call them out - what have you got to lose?

^^^^^That.
If you don't know what you're doing, mess about with it & mess it all up then you might have an expensive problem.
If you are an AA (or other breakdown service) member get them to come & sort it out. Hopefully they will know what they're doing & save you all the bother.
Who knows, they might even fit the new battery for you.

They will, almost certainly offer to sell you a new, expensive battery. But then, if they do, it's job jobbed, isn't it?

[Artsy]

Update.

The car has been back to normal for the last 3 days so, for now at least, I'll continue to use it.

If it fails on me then I'll be getting a replacement battery.

Thanks to all who contributed.