Originally Posted by
niznai
That is surprising.
A battery off the charger is at 8.4 volts, but as soon as you plug it in and drive away drops to about 7.4 and stays there or drops slightly depending how much you use it before recharging. I would suggest you measure your battery with a small load (plugged in the car is fine, the receiver draws about 20mA or thereabouts) to get a more reliable value. At no load the voltage doesn't mean much. Intelligent chargers such as the Supernova (which is pretty much standard around here) place a small load when measuring the voltage they display. You need the same load applied to give you a comparison.
Alright, you got my attention. I charged up a pack and did some testing. Used my charger, multimeter and a pocket voltage checker to verify at various stages. Here's what I found:
Charged to 8.4v
Hooked up to car 8.4v
Powered on 8.4v
Running at part throttle 8.3v
Running almost wide open, heavy load (stiff diff, wheel held) 7.8v
Immediately after running for about 1 minute 8.15v
Resting, rose to 8.3v after 1 minute
I generally check my voltage immediately when I get to my pit table, so we'll call that about a minute.
Not sure why a battery would drop to 7.4v and stay there unless it's been run hard for more than a couple of minutes. Testing with a load tests ability of the battery to deliver power only while under said load, not at rest. I agree that a battery can show lower numbers while stressed, but when we check voltage, we're generally not chasing the car around the track.
