The Battery Bug

* Note. This page is not complete!

Many folks have had trouble with the Aux battery in the Rav4EV (and in the Prius!). They're relatively low-capacity batteries. And since there isn't much expected of them, the assumption was that smaller would be better. But unless that battery is quite healthy, all kinds of crazy things can happen. Charge timer will set but won't stop charging. Car won't start. Car won't charge. You name it - if something goes wonky - the first thing to check is that Aux battery! Enter the Argus Battery Bug - a cute little device that learns the capacity of the battery and constantly monitors it. The device is a VERY fancy Voltage monitor that also detects internal resistance and determines the amount of life remaining in the battery. If the battery loses 50% of it's charge, or determines that it can only hold 50% of its original capacity, the device will beep a warning at you.

I first installed the Battery Bug on my Prius - but since the Aux battery is such a bugger to get at, I installed the unit at the fuse box under the hood. After I checked with the folks at Argus, I moved it to the Rav4EV. Turns out that the device won't work at the far end of a big wire run like I have in the Prius. There's no hope of a valid internal resistance measurement that way. One thing I *did* learn is that both conductors of the included lead wires must be used for the device to function. I had to snip the spade off of one lead to fit it into the Prius.

Here it is, before modification:

After nipping the end off, the two conductors must be connected. Darell recommends (and I'm sure the manufacturer agrees): Don't do this!

Installed in the Prius on top of the main fuse cover. Turns out that this is no good since the battery is on the far end of several meters of wiring. The internal resistance of the battery cannot be calculated, and the display ended up showing 100% all the time. Not much use!

Pictures of the Bug installed in the RAv next... once I find them.

Click for
EVnut.com_home page