Simplified - a battery isolator is essentially 2 one way valves.  There is one
inlet and 2 outlets.  The current flows in the single inlet, and flows out the
2 outlets.  The battery with the least charge gets the majority of the charge
current.  So, the answer is, yes, both get charged, and to the same voltage.

The drawback of this is that the batteries get about .7 volts less max charge.
This can be corrected for if you have an alternator with the D+ and B+
connections.  If you don't have that, the VW solution of a charge relay for the
second battery is better.

tom

On 4 Sep 2003 at 6:54, Gnarlodious wrote:

> Question:
> A battery isolator will block discharge from the starting battery while
> allowing discharge from the accessory battery.
>
> But what if I want to CHARGE the accessory battery AND the starting battery
> at the same time? Will the isolator block the 'backward flowing" current
> from charging the starting battery?
>
> --Gnarlie
>

------
Tom Ring K0TAR, ex-WA2PHW  EN34hx
85 Westphalia GL Albert
96 Jetta GL The Intimidator
taring@taring.org

"It is better to go into a turn slow, and come out fast, than to go into a turn fast
and come out dead." Stirling Moss