Matt,

Think of it as two water balloons hooked to a 'Y' shaped hose. your switch is a valve on the leg of the 'Y' that switches between your tank, driven by a water wheel, and a big 'smart' tank of water (the charger). You run the tank's water wheel untill the balloons are almost, but not completely, empty. Then you recharge the balloons by switching to the water tank. The balloons begin to refill. The 'smart' water tank senses that water is flowing out of the tank and into the switch (and thus the balloons) and everything is fine. As the balloons fill, one reaches capacity before the other and the water flow decreases. The flow is still enough that the "smart' charger still thinks that all is well, but,,, the full balloon begins to rebound and starts pushing water out and into the unfilled balloon, further decreasing the flow from the charger. The charger senses that further decrease flow and thinks everything is full, so it shuts down. The two balloons equalize the water levels, which leaves both below optimum charge, and then begin to leak back into the charger's back end..

I suggest that you setup your switches so that you can charge one batt at a time, if you are using a smart charger. If you use the stock charger, you are better advised to charge one batt at a tim, but you can get away with charging two in parallel, but you'll be putting a strain on the stock charger. See PzrWest's post on cooling mod to the HL stock charger.

splat