2024 Prime being left for 2 months

I learned a tough lesson with my Gen 3. I left my Prius parked for about 5 weeks, because I was using a company vehicle. My 12V battery had a full charge when it was parked, but when I went to start it, it had such a low charge that it vibrated the relays. Only giving it a 200 amp boost got it to go into "Ready" mode. I was fully expecting a massive electrical system failure as a result, which thankfully never happened.

My Gen 5 drains the battery much more quickly. Several times, it would not go into "Ready" mode because the battery had gone below 12 volts, after only about 2 days. Sadly, just getting the dash lights to come on will not charge the 12V battery to allow you to start the car (as it did with my Gen 3). I stays in a error state, and a battery boost is required.

The dealer replaced the 12V battery, but that didn't solve the problem. My 2024 Prius drains the battery very quickly, depending on the wireless connection, and whether it's doing a firmware update or not. My remedy was to install a 2 amp battery maintainer, which I plug in whenever I park the car at home. No dead battery since.
Prior to this however, my battery once went flat in about 2 hours during a firmware update. A lithium booster pack was required to start the car. I also installed an auxiliary 100 Ah lithium battery for periods away from home, when I can't use the battery maintainer. It is connected in parallel with the standard 12V battery, through a "smart battery isolator" which insures that the aux battery won't deplete from parasitic drain. There is a high amperage bypass switch which would serve to provide a boost, but so far it hasn't been needed.

 

Traction battery around 60%.

 

I'd hate to risk my traction battery by leaving it parked for so long. There was a posting on here a few years back, by someone who bought a Prius from another country, and it arrived with a dead hybrid battery that wouldn't take a charge. I can't recall hearing about the final outcome.

 

For that duration I'd either disconnect the 12 volt battery's negative cable, or keep it on a smart charger.

 

I don't pretend to know exactly what caused my problems with either battery, but I am loathe to leave my Prius parked for long unattended.

 

check the o/m. in my 2012, it said to drive it until the engine comes on in hybrid mode, and leave it there.
however, they didn't define a specific amount of time you might be leaving it for, just 'long periods' or something like that.
in my bev, i leave it at 30% when we go south for 3 months in the winter.

 

Disregard, I was recalling NiMh best practices.

Checked the 2024 owners manual (page 113) for the lithium pack: "Leave a low level of charge in the hybrid battery (traction battery) when leaving the vehicle undriven for a long period of time. After confirming that EV mode or AUTO EV/HV mode has switched to HV mode, turn the power switch off."

 

If you're going to follow your owner's manual, why are you asking here?

 

25% on the lithium-ion is optimal. So, 30% is OK.

Make sure that you connect a battery maintainer such as a Noco Genius; otherwise, you will come back to a dead 12-V battery.

 

Max charge on hybrid battery and max charge on 12volt battery would be ideal. Also disconnecting the 12v would be wise if it's longer than 6 months.

But because its a brand new car you really don't need to do anything at all, it'll be fine. It's still under warranty too so it's on Toyota to deal with it if anything goes wrong.

 

No, keeping at the maximum charge or a high charge is detrimental to the lithium-ion battery. It would result in serious battery degradation if you kept it at the maximum charge for two months. That’s why you need to use the charge schedule or such and charge immediately before you drive.

Yes, you can disconnect the 12-V battery, but using a battery maintainer is a better option. For lead–acid batteries, keeping them at the maximum charge is the best.

 

i didn't ask. i was replying

 

Lol, That's why max charge on lithium packs are a significantly lower percentage of the 100% by the very nature of the BMS design.

My point is in some case Lithium-ion packs power some safety components that are always on regardless of 12v power and while I don't know if Gen5 has any of those systems, if they do it'd be wise not to park it for months on a near empty charge.

 

This is common knowledge.

Even with a 10–15% upper buffer, it is still too high and detrimental.

That is why the owner’s manual recommends bringing the lithium-ion battery to 0% SOC before storage and using the charge schedule for daily driving.

I wouldn't bring it to 0% SOC but keep it around 25% SOC.

Regarding your question whether the lithium-ion battery is drained while the car is not driven, the answer is no.

Here is the excerpt from the owner’s manual:

2024 Prime being left for 2 months | PriusChat

 

Yes, but again 0% is not really 0% It's simply where the battery power curve drops suddenly and there's no viable amount of power left after that drop point. But there's still enough power in that pack to kill you or power the vehicle an extremely short distance.

 

Yes, of course, it is the lower buffer (about 10–15%) plus the HEV allocation (about 1 kWh). So, for Gen 4, it is about 25%, and for Gen 5, it is about 20%. Therefore, a 25% SOC would be about 40–45%, which should be OK in terms of battery longevity. I wouldn’t keep it at a higher SOC for long-term storage.

 

Actually, I would somewhat ignore the Toyota recommendation, which is based on and a manual carryover from the non-plug-in Prius, not the plug-in Prius—it is laziness on the side of the Toyota manual writers.

If you Google “ideal lithium-ion storage SOC,” you will see that the answer is universally about 40%.

For the non-plug-in Prius, leaving the car on until the ICE kicks in works because it would bring the SOC down to about 40%, which is ideal.

For the plug-in Prius, the same thing will result in about a 20% SOC—considering the lower buffer and HEV reserve—which is OK, but not ideal. If you leave it around 20–25% meter-gauge SOC, the actual SOC will be about 40–45%, which should be ideal.

In any case, never leave it for extended periods at over 60–70% meter-gauge SOC to avoid serious battery degradation.