Cold weather, trikle chargers?

[Mistel]

We had a cold snap here in Toronto and the wife couldn't start the 85 300TDT and I went out and tried my diesel truck and could hear it was not going to start. Our first problem was they were not plugged in, but the other problem is that the battery capacity falls as the temperature goes down. I was thinking of wiring a trikle charger up to the block heater plug so that when you plug in the car you plug in the charger as well. Does this make sense or would it be waste of time? The truck has a good block heater so it may not be worth the effort but the Benz has an aftermarket pad heater on the oil pan that doesn't work great.

Thanks

[Simpler=Better]

You should get a lower radiator hose heater for the Benz. IIRC, $15 on ebay for a 1.5" heater and a fairly short install time.

IF you did wire up a trickle charger, you would want to wire in a continuous-duty normally-open solenoid and a continuous-duty normally closed solenoid in with the charger so that:
1. When the car is on/off and the charger is unplugged, the charger doesn't connect to the battery
2. When the car is off and the charger is plugged in, the charger will connect to the battery.
3. When the car is on, and the charger is unplugged/plugged in the charger will no connect to the battery.

Battery->N/O Solendoid(powered by charger)->N/C Solenoid(Powered by alternator)->charger

Or just remember to take the clips off the battery before starting.

Also, you should set your signature to contain you car's model so you don't have to retype it each time you post

[rwthomas1]

The way I understand it the cold actually slows down the chemistry in the battery reducing its capacity so I don't think that adding a trickle charge will improve things. Unless the vehicles are driven rarely and then yes, at least the batteries will be at maximum charge when needed. Daily driven cars should be fully charged from use. That said I have used "Battery Tender" brand trickle chargers on motorcycles and such and they work as advertised. Plug it in for cold weather starting. RT

[Matt L]

A charger will warm the battery, and it will make a dramatic improvement given that all other parameters remain equal.

[uberwgn]

Battery warmers here:

http://www.wolverineheater.com/products.shtml

A block heater or coolant heater will certainly help things during extreme temps. Having a battery in top condition is imperative, of course.