Best 12v battery replacement? Particularly to use with power inverter?

I would use two Toyota agms with the second isolated through an rv isolator of good quality. Someone posted the second battery installation in the extra storage area opposite the primary battery. When in Ready both batteries are in parallel for charging and load sharing. When not in Ready the second battery takes the load, ensuring the primary battery is not discharged.

 

Not too surprising; starting the Prius just doesn't take that much. Running the brake pump just before starting takes more. Sometimes if I have an inadvertently discharged battery, I'll be sure to wait for the pump to stop, and a few moments more, before starting the car. In a couple more dire discharges, I got the car started by pulling the brake pump relays first, and putting them back after the car was in READY.

As long as you are doing this with the car in READY, the power to run the inverter isn't coming from the battery, and so your selection of a battery doesn't especially have to be tailored to it.

You could check me on that though. I would suggest attaching a voltmeter across the battery terminals themselves, while the car is in READY, and note how low a voltage you see between those two points when the car is READY and the microwave is running, or the Instant Pot is heating. (I assume you do not run the two simultaneously.)

Those readings would be interesting, if you were to post them here.

Edit: I first wrote "note the lowest voltage you see", which could suggest using a min/max setting on a meter, but I'm really more interested in how low the steady voltage gets, not so much how low it might go for a mere moment when the magnetron cuts in, etc. It wouldn't surprise if some peaks like that represented a net outflow from the battery, but for a brief enough time to be effectively ignorable.

 

I believe the max safe continuous current for the DC-DC converter is about 1200W, so as long as you're only running one appliance at a time, you'd be fine and the battery would only smooth out slightly higher spikes, meaning any battery appropriate for the car will work. If you're running both pieces of equipment at a time, not only do you risk blowing the DC-DC converter fuse (or worse), but your battery will only have about an hour to full discharge. Obviously you don't want to get anywhere near full discharge, and your tolerance will decline as the battery gets older, so you probably shouldn't be running both pieces of equipment for more than a couple minutes max.

Also, your existing battery is still starting the car because it really only has to boot some computers and the HV battery actually does the hard work of starting the engine. My battery has tested as being "bad" for the past 2 years.

 

True, a battery may test as too "bad" to start a conventional car for some time and yet still start a Prius most of the time. On the other hand, it still does eventually cross the line from "will start the Prius most of the time" to "won't start the Prius anymore", and a lot of people find it sudden and unexpected when that happens, because they didn't have the same advance warning of slow rrrWrrrr-rrrWrrr-rrrWrrr starts they would have had in a conventional car. It just doesn't start one day, and it's still inconvenient if that was the day you were trying to make a departing flight.

I find the sound of the brake pump to be something worth listening to when getting in the car. It will do a pretty good impression of a dying wind-up toy if the battery isn't well charged.

 

That is not the battery voltage; it is the charging voltage......which says nothing about the health of the battery itself.

The best battery in this circumstance would be a "deep cycle, AGM" of a larger size than the OEM one.
They are often referred to as "marine" batteries.
BUT that won't conveniently fit where the OEM battery was. And the posts might not match up with the cable ends either.

 

That's largely why I suggested two batteries with an isolator. No need to reinvent the wheel. You could functionally beta test a high capacity lithium battery with built in battery management to emulate an agm. But a dual battery system is better for rv style use and would cost less. When the car is off you are not discharging the factory 12v battery with your extra loads. I suspect your "everything off" parasitic load is excessive with all the extras such as frig, interior lights, wifi repeaters and computers.

 

Is this number from a voltmeter built into the inverter, or your own separate meter? If your own meter, where exactly were both probes at the time of the measurement?

Do you have a kill-a-watt meter or other similar reading of what the microwave actually draws? I believe microwave advertised power (700 watts) tends to be the microwave output of the magnetron.

 

Yes, it probably IS.
BUT......you need to get a handle on the difference between battery voltage and charging voltage.

The measurement that you quoted indicates that your applied load is TOO MUCH for both the charging inverter AND the battery combined.
A bigger battery might help some but I would be worried about frying the inverter.......and that would be $$$ to fix.

 

Don't know. Probably not.
Certainly not one that will be an exact replacement.
The whole idea is to get one that is BIGGER.

 

This is the 85AH battery that I use, now have two in my car, each running a separate 2000W pure sine inverter. Make sure yu use 0 gauge wires, the Prius doesn't work well with cables any smaller when using an inverter.

Custom Battery and Inverter Cables for the Win! - black_jmyntrn

Replacing an OEM 12v battery with an 85AH battery is a success! - black_jmyntrn