exchange 12 volt battery?

[windstrings]

Has anyone tried using a NiMH battery or even a 12 volt configuration of lithium?

I keep reading all these stories of batteries running down.. aside from installing a solar trickle charger.... maybe adding another battery somewhere and just connect the two with wires in parallel?

[Frank Hudon]

how about a gelcell 12 volt battery, no venting problems, and more AH capacity. So what if the one time cost is slightly high the OEM battery isn't cheap either. Anyhow that's my plan when it comes time. No sign of that time yet, left the Classic for 9 day's hopped in and it fired right up. As the lighter socket is live all the time I had plugged my volt meter in and when it started it said 11.7 volts. So no where dead. Sigh guess I'll have to wait till next year. Or the one after that.

[windstrings]

Originally posted by Frank Hudon@Nov 4 2005, 12:25 AM
how about a gelcell 12 volt battery, no venting problems, and more AH capacity. So what if the one time cost is slightly high the OEM battery isn't cheap either. Anyhow that's my plan when it comes time. No sign of that time yet, left the Classic for 9 day's hopped in and it fired right up. As the lighter socket is live all the time I  had plugged my volt meter in and when it started it said 11.7 volts. So no where dead. Sigh guess I'll have to wait till next year. Or the one after that.

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Humm.. .how about
1. storing the gelcell it in a different place.
2. Hooking it together with the lead acid cell via wires "in parallel".. (+ to + and - to -).
3. Installing a diode "not sure how many amps would be needed" that would allow electricity to only go from the 12v lead acid "to" the gelcell, so as to keep it charged while the car was running, but the diode would prevent the gelcell from discharging as the lead acid would be pulled upon by the car acessories while off..... (The get cell could not discharge.)
4. putting a little "throw-switch" inline "in series" that overlooks or basically bypasses the diode. (You would need to manually go back to the battery and flip the switch.)
5. This switch would allow energy to go back into the lead acid battery thereby giving you an jump start should the lead acid ever go down?
6. If you had a trickle charger too.. "solar or otherwise", it would keep both batteries charged... just make sure to hook it to the lead acid side so the diode wouldn't block charging of both batteries!

Now if the car accessories ever accidentally drained the lead acid, you would have an instant backup!..
Hey.. you could still replace the lead acid with a gelcell for good measure if you like and have a gelcell backup... MIght save you a jumpstart problem on a cold rainy night!

[Frank Hudon]

diodes are not an option as the voltage drop across them in a charging circuit prevents the battery from ever becoming fully charged. Simplest solution is one of those jump box-booster units. If the battery in the car goes dead just jump it like a normal car.

[andyprius]

Hi, I enquired to this subject about a year ago and Frank ( I believe ) was nice enough to forward a nice schematic. Since I'm no longer into electronics I did not bother. But, did buy a small gel cell ( 7 AMP ) and charge it from time to time thru the socket, on a trip. Did run the car on it alone for about 6 miles for a test. Seem to support the Computer fine. One of the Senior Advisors also warned me that a large current demand could be made and burn up the 7Amp battery as well as some Prius electronics. So...it'sprobably OK as a temp solution.

[windstrings]

Originally posted by Frank Hudon@Nov 4 2005, 12:32 PM
diodes are not an option as the voltage drop across them in a charging circuit prevents the battery from ever becoming fully charged. Simplest solution is one of those jump box-booster units. If the battery in the car goes dead just jump it like a normal car.

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There is only a 1/2 volt drop.. depending on which type you use.. at 12 volts thats only a little waste. MOst charging systems overcharge alittle more than needed anyway, that would leave plenty volts for the second battery.

[windstrings]

Originally posted by andyprius@Nov 5 2005, 01:45 PM
Hi, I enquired to this subject about a year ago and Frank ( I believe  ) was nice enough to forward a nice schematic. Since I'm no longer into electronics I did not bother. But, did buy a small gel cell ( 7 AMP ) and charge it from time to time thru the socket, on a trip. Did  run the car on it alone for about 6 miles for a test. Seem to support the Computer fine. One of the Senior Advisors also warned me that a large current demand could be made and burn up the 7Amp battery as well as some Prius electronics. So...it'sprobably OK as a temp solution.

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I could see if you had the battery isolated from the inverters input of 1400 watts worth of 12v power to assist?
I wouldn't ever suggest to use the battery "by itself".. even the original battery would be risky for that means. Normally the system inverter keeps the 12v charges while its also carry the load of the accessories?
When the car is off... the worst that could happen is things would cease to work.. I don't think any hardware that is voltage critical in sensitivity is hooked to the battery's accessory side.

But it could still be a good backup, but you would want to use it as a "jump" to the regular battery so once all is up and running.. your whole system is intact.

[tumbleweed]

Threre seems to be no way of predicting a failure of the 12V battery while it is in normal operation. With a normal car battery you can usually tell because the starter turns a little slower or the headlights are a bit dim when the engine is off, etc. My guess is when these things go they usually lose all or almost all of their capacity but when fully charged the Voltage is just fine.

I think you could remove it from the car and do a load test on it. All you would need would be a load resistor (even a light bulb would work) and a multimeter. The best setup would be a big rheostat a Voltmeter and an Ampmeter. Discharge it and find out how many Ampere hours it had left in it. Just take it down to 10.5 Volts (1.75 Volts per cell) at it's 8 hour rate and see how long that takes. I think if it got down to 60% or 70% of it's rated capacity it would be time to replace it.

We would need to know how many Ampere hours it is rated at, divide that by 8 and compute what size resistor we would need. Of course to be completely accurate you need to decrease the resistance a little as the Voltage drops but even if you didn't do that you would get a good enough answer.

Anyone see any problems with this?

[windstrings]

Originally posted by tumbleweed@Nov 5 2005, 04:08 PM
Threre seems to be no way of predicting a failure of the 12V battery while it is in normal operation.  With a normal car battery you can usually tell because the starter turns a little slower or the headlights are a bit dim when the engine is off, etc.  My guess is when these things go they usually lose all or almost all of their capacity but when fully charged the Voltage is just fine.

I think you could remove it from the car and do a load test on it.  All you would need would be a load resistor (even a light bulb would work) and a multimeter.  The best setup would be a big rheostat a Voltmeter and an Ampmeter. Discharge it and find out how many Ampere hours it had left in it.  Just take it down to 10.5 Volts (1.75 Volts per cell) at it's 8 hour rate and see how long that takes.  I think if it got down to 60% or 70% of it's rated capacity it would be time to replace it.

We would need to know how many Ampere hours it is rated at, divide that by 8 and compute what size resistor we would need.  Of course to be completely accurate you need to decrease the resistance a little as the Voltage drops but even if you didn't do that you would get a good enough answer.

Anyone see any problems with this?

NO problems per se.. just for me not too practicle... I figure the lights in the car are a good test.. either they are dim, or they don't work at all... having the backup to jump would confirm and cure all of that, then at your leisure you could replace or condition the battery.. usually replace is the best option for lead acid if they have been charged properly and they are down.. they are ususally bad.

[tumbleweed]

I agree, if it is weak replace it. Does anyone know how old the batteries were that failed? I would think a battery such as this should last for, what? 4 or 5 years? I usually get 5 or 6 out of a good car battery.