Spare Hybrid Battery Maintenance

We drive our Toyotas far beyond any warranty. So I've bought a spare hybrid battery from a wreck, in case I need one at, say, 200,000 miles.

But I don't know if it's any good, I don't know whether to store it on a charger or let it self-discharge, and I don't know how best to recharge it when I need to use it several years from now.

TESTING IT:

The battery pack apparently has at least one interlock to shut it off when it's outside the car, so I can't just measure it to see if it's any good. I can't charge it either, without knowing the terminal polarities.

Toyota diagrams don't even say which of the terminals is positive!

Toyota mechanics and managers are so spooked by the 273 volts that they sacrifice virgins over the hood before they'll work on it. Getting information out of them is futile - they don't know either! What's worse, they wouldn't tell you if they did, for fear your lawyer will sue them for electrocution. Telling them my experience with 4 million volt power supplies leaves them unimpressed. 273 volts is already voodoo territory.

If anyone out there has a diagram of just how to cheat the battery interlocks so I can at LEAST measure the voltage on a battery outside the car, I'd be pleased to know about it.

CHARGING:

Once I get the battery terminals alive and identified, I can figure out for myself how to charge it. A cheap rectifier bridge across the 220 volt clothes-dryer line driving the battery through two 100 watt bulbs should work fine as long as you don't overheat the darn thing or flummox the battery ECU - which tries to equalize the cell voltages.

STARTING A DEAD PRIUS FOR UNDER $600:

With a dead hybrid battery, but with a good 12v battery, one should be able to roll it down a long hill to regenerate the hybrid battery enough to start the engine and revive the car. The car CAN be put into a state that allows this, but it's tricky to do, and the car's interlocks normally prevent it. I've noticed that, when you run out of gas, and the engine stops, the control system thinks the engine is dead for good. Even when you get to the gas station on battery power, recharging downhill and discharging uphill all the way, and you leave the ignition on while you fill the tank to the top fuel indicator bar, the control system will not automatically re-start the "dead" engine until you reset it by turning the ignition off first. Before you reset it, it WILL regenerate the battery if you coast it downhill.

What I'd like to do when I install my discharged spare hybrid battery - four years from now - is somehow put the control system into that state, where the regenerator is enabled but the system won't automatically try to start the engine. Then I'd roll it down a hill to put a small charge into the hybrid battery, stop; turn the key off to reset everything; then use that small charge to start the car. Then the battery will get recharged and I'll be fine.

To do that, I have to make the control system think I've just run out of gas, and that I've run the battery down a bit. Once I convince it of that, it will allow me to roll down a hill to recharge. It IS possible to make it think that way, by killing the engine; but you can't kill the engine if the battery won't start it first!

Does anyone know what kind of interlock cheater would enable me to do that - to fool the control system into "READY-except-for-engine"?

Another way to do it MAY be to apply a 273 volt power supply to the battery terminals just to start the car up. It shouldn't need much power - maybe one HP. But the control system might not like like it. There are some connectors on the battery pack that look like they're there to do just that - but Toyota isn't talking.

ANOTHER POSSIBILITY:

There's an outside chance that Toyota has done something clever, and the customer support people just don't know it. If the Toyota enigneers were smart enough to include a cross-switch to start the engine from the 12v auxiliary battery when the hybrid battery is low, there would be litttle problem starting the car with a discharged hybrid battery - as long as the 12v battery is OK and there's gas in the tank. This is because the electric motors are designed to generate about 44 HP at perhaps 4000 RPM. At that maximum, the full 273 volts must be applied to the motors. But motor speed is proportional to applied voltage. If only 12v were applied, the motors could still turn the engine at about 175 RPM - enough to start it.

If that were true, it would show up in Toyota's procedure for starting a Prius with a discharged hybrid battery. But just try getting something THAT COMPLEX out of a Toyota dealer spooked with 273 volt voodoo!

TOYOTA:

I've been struggling for over a year with Toyota to pry loose information on how to recharge a dead hybrid battery, and I've so far hit such a brick wall that I'm thinking it's time to file suit for the information. You know the routine - from 800-number to 800-number and back around again, bouncing between very polite people very conerned about your problem, but who don't know anything at all - and have no one to ask but each other.

Let me know if YOU know anything!

- phil Harvey