mxt_77

So, I don't currently have a battery charger, but I know that it is recommended to hook one up to the battery while doing a compression test so you will have consistent numbers.

Can anyone make recommendations on the type of charger to get? What kind of amperage should I be looking for? What is the difference between "Manual" and "Automatic" chargers? I've seen some that have different amperages for trickle charge, fast charge, and "start" mode. Do I need all of these things?

xviper

I've never heard of this. I think it's important to have a well charged battery when beginning a compression test so that you get good, uniform cranking. If your battery is old or weak, then you might need to use a charger that will have enough juice to actually crank a car with a dead battery. Most chargers won't have this capacity. The ones that do will have a setting on them that says it's for starting a car. An "automatic" charger is one that knows when to shut itself off when the battery is fully charged. These too, will say if they are designed to start a car with a dead battery.

mxt_77

The ones that I've been looking at have the capability to start a car. However, I assume that they'll be putting out a lot of juice when they are in that mode, and I'm wondering if that will be harmful to the battery (particularly if it doesn't really need chargin). Maybe the automatic mode would be useful for protecting the battery in this scenario. ?

xviper

If your battery is in good shape, do the compression test without the charger. When you're done, then charge the battery back up in automatic mode so you don't overcharge. You are only cranking the thing over for about 5 seconds X 4. I'm sure you'll turn off the ignition in between cylinders anyway. A good battery can take this no problem. Turn off all other power requirements when doing this - stereo, dome light, HVAC fan, etc.

Gernby

"Starter" chargers only pump the big juice when there is a significant amount of current draw. I have one if you want to come by. Actually, you can just do the compression test here. Maybe we could even test my car and compare the results. One thing that I've done to even out the effects of cooling and battery drain is to retest the cylinder that I tested first after testing the others to see how much the result changes.