Is adding a second battery possible?

I would never call such a project impossible but it would be a very, very tall order as a DIY project.

Three points:

1. If you want to do this for extreme bragging points and cool-factor? I wish you the best- this would be big. Conversely, if you want to do this to save time, money or other resources, I urge you to stop now. You will rapidly exceed the affordability of PHEVs already available, to say nothing of those coming soon, all without ever matching their capability.

2. Even doubling a Prius battery is not in the same zipcode of battery capacity as a typical PHEV. A Prius battery has about 1.3kWh capacity. Most storebought PHEVs these days offer 8kWh and up. So I would (not very seriously) suggest adding 3-5 more HV batteries as a starter goal. Obviously that vastly complicates things and yet still doesn't make much of a PHEV range-wise.

3. The Prius Prime PHEV also includes a trick clutch between the combustion engine and the transaxle. This device allows the car to drive at highway speeds using electric power exclusively without also forcing the engine to spin in deadhead mode. Your car doesn't have this clutch, so your electric-only efficiency would suffer badly above roughly 40mph.

 

Assuming you have a generic Prius NIMH you could just charge your battery up, reset the computer and on your commute the car would burn off some of the three to five EV miles you built up.

understand this wears the battery out faster and may cause your car to freak out with CELs and other unenjoyable nonsense

another method of mild range extension is modifying your 12 volt battery to be a 14 ish volt deep cycle, this shuts off the dcdc and drives 250-600 watts to your battery.
take care not to exceed the cars maximum voltage while recharging (hard to do) and it does have a real effect on fuel economy similar to an alternator delete.

in terms of having two NIMH batteries it’s a fire hazard so don’t bother.

I recommend visiting ecomodder for actual real world mods that work to get better economy and not high hanging fruit that wastes time and money

good luck
Ryan

 

Even if you added enough batteries to have useful range, you'd still have the speed and acceleration limitations that would make the car unusable for anything more than residential speeds. The MGs and inverter don't have enough power handling capability for highway speeds nor can the MGs spin fast enough because of the gearing and construction.

 

It's Hybrid Synergy Drive....don't mess with the Synergy.

 

no

 

THIS.
All the computer systems expect to see a certain HV battery in place.
Having one that is drastically different would likely cause DRASTIC results.

So the answer is: NO. Not practical.

 

prime only achieves a small amount of mpg's over lift back, if you're not using wall power, and will not run in ev mode if the wall charge is used up.

and yes, compared to lift back, prime battery is umongous

 

IF it was possible, and I won't say that it isn't, I would expect the only practical way of doing it would be to add a duplicate battery that could be electrically switched/swapped.

 

You could alway get a Prius Prime

 

Think about that. How do you run in electric mode? By supplying power from a charged battery. How do you charge the battery? By running the engine on gasoline, or by harvesting momentum. How do you harvest the momentum? Get the car rolling, then apply regenerative brakes. How do you get the car rolling? <loop to beginning>

All of the energy comes in through the gas filler, and then some of it gets recycled via the regen function. But only some, due to efficiency loss. Hypothetically you could make a Prius even more fuel efficient by eliminating the electric end of the hybrid powertrain and just coupling the engine to the wheels. Less weight to carry and no conversion losses in the electrics. Downside: it would be almost undrivable and hopelessly incompatible with traffic and drivers' expectations.

In a sense, the real secret of Prius fuel efficiency is the tiny gas engine. It's too weak to power a Prius-sized car alone, but when combined with the electrics of the HSD, it gains driveability.

 

no worries

nothing stops you from charging that battery for a small economy gain.

many grid charge batteries to get life out of failing packs.

and again

ecomodder.com

Darin, Neil B and Ben Nelson have all been there done that, start a thread there

 

Some electrical issues. If the batteries are in parallel you need twice the current to charge them, you don't have it.
If the batteries are in series you need twice the voltage to charge them, you don't have that, and it is unlikely you can get it.

The other choice is PHEV one battery, so you have more current. At that point the cheapest way it to buy a PHEV.

There were a whole flurry of kits to do this in 2004, but those companies are went broke paying out liability claims.

 

OR you need the same current for twice as long.

 

I've been tinkering with the idea, but in by no means think I would ever try it. From reading what others have done with the Prius, I do think it's doable.

The thing for me is that when driving in the mountains it makes sense to have a bigger battery to adsorb the down hills and help push the car up the up hills. But I don't go over mountain passes that often to even come close to making such a project worth it. If I had to go over a pass every day, I'd probably get a PIP or Prime instead.

 

The NIMH battery holds such little charge when they are 5+ years old. It would be flat by the time you leave your driveway

 

Total bunk.
Where DID you get that idea ??
We have lots of users on here who are still going strong after more than 10 years.