I think you would be better off buying 2 sets of 3 batteries and simply rotating the full sets in and out for charging.
Chris H.
Thanks Chris. I assume from the above you have a concern charging a single battery while hookup in series? I have been researching switches and think I have answered my own question in a way, but I welcome your corrections.
Three new fully charged 6v batteries give 19.2v. After 2 days of playing all batteries will be above 6v. Remember one gets charged every night. I am a bit over the target voltage of 18v for the B1 but this gives me a little room as the batteries age.
I want to hide these batteries in a box and use switches for on- off -charge. I wonder if three DPDT would not accomplish this? These are the versions that have on-off-on positions. The last "on" position is to the charger always plugged into the wall. If I use all the "off" positions I turn off the B1 and break the series.