Charging another car's battery

Can? Should?
You probably can but Toyota’s party line is no.
Maybe disconnect the negative on the Prime battery so as to electrically isolate it. Remember the Prime battery doesn’t really crank the engine. It just runs the electronics, headlights etc.
so cranking a actual engine might be a shock to the system. If you end up frying the Prime it would make a AAA call cheap.

 

Sure, go buy a jump pak, and use it. $40 to $70 is SO much cheaper than the $2500 you risk paying to fix your inverter.
2018 Toyota Prius Prime Inverter assembly, with converter. Electrical, assy - G920049107 | Savannah Toyota, Savannah GA


Portable 20000mAh Car Jump Starter Engine Battery Charger Power Bank Vehicle Battery Booster - Walmart.com - Walmart.com

I am not sure what is local to Charotte, but everything should be.
Sears.com

https://www.napaonline.com/en/p/SORCS1100?partTypeName=Battery+Booster+Pack&keywordInput=jump+start

 

I've used a Deltran Battery Charger Plus on my Prius V (when I had it) plus 2 different Acuras, works great and didn't cost a lot.

 

I’ve never tried it, but I can’t think of any reason why it wouldn’t be possible: The Prime’s 12V battery, as far as I know at least, is an off-the-shelf lead-acid car battery. Such batteries have to be kept charged, so it conceptually should be able to start any ol’ car.

The only reason I could think of why it might not be advisable would be if the Prime’s 12V charging system would be super wimpy (having no need to be beefy), and thus would take a really long time to recharge afterwards.

However, if the user manual says not to, then probably best not to...

 

Sure.
Also if the condition of the "dead" battery really is unknown, you could be connecting your 12 V system to a DEAD SHORT.
If you do that, the repair cost to your Prius might be MORE that the vehicle that originally had the problem.

Of course, you could completely disconnect the Prius 12 V from the car and then just it to jump.
If the sick vehicle starts fairly quickly, there should be no harm to the second battery.

But I vote for using the AAA benefits that you are paying for.

 

The 12V battery in a Prius is not designed to crank a gas motor, so I would say bad idea to use it to jump start a car that needs a battery to crank the gas motor. I'm pretty sure this is spelled out in the manual.

I wouldn't even use the Prime's battery to trickle charge the CRV battery. Either buy a viable battery maintainer for the CRV, or take the CRV battery out and bring it to a battery shop and have it tested and charged. Depending on how old it is and how low the charge got, you may not even be able to save it with a recharge. Only a battery shop can tell you that.

 

The computerized inverter used to charge battery was not designed for that. Doing that when the manual says not to would void any warranty for repairs needed for the charging circuit.

 

No way would I connect my Prius to another car and ask it to crank that engine with a battery sized to just turn on computers and close a relay. It might work and not damage your multi-thousand dollar inverter, but then again, I might get away with crossing a busy street with my eyes closed. Neither action is worth the unnecessary risk.

Best answers are already given. Use either a jump pack or a charger to breathe some life into the CRV's battery. Every car owner should own at least one of those devices if not both. Don't have one? Get one, and then you'll be able to deal with this situation next time it happens. And it will happen again.

 

“Clothe” the battery?

In any case, to the degree that you’re using the Prius Prime’s 12 battery to start the other car, it’s probably OK, as long as the battery doesn’t discharge too much.

However, as the other car starts, it’s alternator will suddenly kick out 14ish volts onto the Prius Prime’s battery terminals, probably along with spikes to higher voltages. That’s not a problem for the battery itself, but it probably is a problem for the Prius Prime’s charging circuitry.

 

Gen-4 Prii, unlike Gen-2 at least (and I think Gen-3 as well), use generic, off-the-shelf car batteries. Although generic car batteries have vastly greater Specific Energy and especially Specific Power than is needed, it’s ultimately simpler for everybody to just use a generic part, rather than having to supply, warehouse (etc.) a specific-purpose part.

As Sam Spade 2 pointed out though, when you jumpstart a car, you’re not only connecting the dead car to the good car’s battery, but also to the good car’s charging system, so there’s no guarantee that they charging system is designed to accommodate that.

 

iPhone correction? Poor typing? lack of coffee?
Take your pick

 

But I think the cranking capacity is lower since that is an unnecessary expense. Either way, since Toyota says not to do it, do not do it unless you wish to sacrifice the vehicle's warranty. I believe the inverter is considered part of the Hybrid system for warranty purposes.

 

So then, you believe it not to be a generic car battery? I don’t claim to know for sure, but it sure looks generic.

I suspect they gave up on the pointlessly-specialized 12V battery biz, and just switched over to a cheap, generic battery, easily available everywhere, even though it has vastly more “cold cranking amps” than it would ever need.

But, yeah, I wouldn’t recommend trying it, unless you completely disconnect the battery from the Prime, and even then, only for a short time. And if it is not a generic car battery, then definitely not.

 

Also no guaranty that the polarities will be right unless you do it yourself and double check before completing the connections. Whereas modern chargers and jump packs check the polarity before they energize the cables.