So I just bought another rehab prius 2007 with 237k miles Checking through the self diagnosis menu I see that the 12v battery has the following conditions: 12.2v systems on, engine off drops to 11.8v when the engine is powered on 14.0 - 14.1v when the engine is running but never exceeds that I have no history on the car, so I'm just trying to get an idea if I should blindly replace the battery or if I'm good to go. I already have an appointment to get the HV battery replaced under warranty
Warranty on the battery? Didn't know they are transferable. Your 12v probably only needs a good charge, or you driving the car for a week should do the job
Hook it up to a smart charger, something in 3~4 amp range, let it run to completion. If it stalls, never completes, say after 12 hours, or shows some sort of error code, time for a new battery. Assuming it does complete: drive the car for a few days, then test battery with Solar BA5 or similar; it'll give a "verdict".
The factory one is. But it certainly is NOT good for 237,000 miles. I suspect that his 12V is on the way out too. I certainly wouldn't trust it with those numbers.
The OP mentioned reading these voltages "through the self diagnosis menu", i.e., on the MFD. Given we know that measures voltage a bit over half a volt downstream of the battery (in ACC or ON; in READY it's actually upstream), those numbers are splendid and my advice would be to enjoy the car, unless it has given you any specific reason to question the battery.
Get brocolli. Eat or throw away brocolli. Use rubber bands. My Milwaukee actually has clips for the probes on the back, but as far as I can see they're useless. I've tried various permutations, wrapping the leads this way and that: hopeless: get brocolli.
IF......you wrap the leads around the case the other way, around the narrow sides.....they will soon take on that shape and will pretty much stay put with NO extra tie-wraps at all.
12 V, normal resting voltage for most lead acid batteries. The higher charge voltage is for overcoming the internal resistance of the plates, so the charging requires 14 + volts. If you read under 12 V when the battery is not connected, then you might consider replacement, but always perform a good charge cycle, depending on usage. a long rest period will drain every battery over time. Solar chargers are great, and I use this method a lot. The Prius shuts off the 12 volt ports when you shut down, so this is not an option. My Olds Silhouette, did not suffer this, so I left my panel connected full time...never had a problem with the battery. Heat is the worst enemy to batteries, and living in Arizona, one must be aware of this failing. If possible, always try to park where the hood is covered by foliage or something. And no, this 'trick' fails on Prius...there is no battery under the hood. Proper care and feeding of your batteries will provide long life, and few worries. Live long and prosper! Spock...out.
Thanks everyone for the advice. to answer the HV battery is aftermarket, but the previous owner made the appointment for me and the company agreed to take care of the swap - pretty cool! as far as the 12v, I will have to check if it's aftermarket or not. But I came across a great deal on a GS Yuasa which is why if the 12v were borderline, I would jump on it!
Wisdom this was NOT. Nominal fully charged resting voltage for "most" lead acid batteries is 12.6; higher for an AGM. 12.0 is about half discharged. It does not take 14+ volts to charge. Float voltage is about 13.2 and anything above that will charge a little; the higher the voltage, the more charging.
