How/when to recharge batteries

It depends on the battery chemistry.

If yours has SLA batteries it's best to keep them fully charged at all times. The charger should stop charging if it thinks the batteries are fully charged. Charging at opportune times during the day is a good idea.

If yours is LiPo that chemistry is less finicky about staying fully charged. Charging while you're out is still a good idea as it extends your range.

if one batteries dies you will get aprox 1 to 3 miles .

What is an "optimizer"?

Is it like being sold a "pound of compression" for an ICE vehicle?

Batteries installed, charged, and disconnected so there is no external drain ... is probably optimal for a "short" vacation.

Long term SLA storage might involve periodic trickle-charging, perhaps on a timer.

Is it OK to leave batteries uncharged for a couple of weeks while on holiday. Obviously they'd be left at full capacity.

I think the best advice for lead-acid batteries is to store them fully charged. However, once they are fully charged, there is no need to leave them connected to the charger, since they will self-discharge rather slowly.

Disconnected means the battery pack is not connected electrically to anything that would drain the pack. Usually there is a circuit breaker, or one can just disconnect one "end" of the series of SLA cells that make up the Pack.

But, mounted in the bike is OK, out of the sun and weather (if possible) is good.

They look like a solid company! I hope you're looking at the http://www.powercharge.dk/default.asp?lang=en version. You say "'optimizers'". Does that mean you have bought one for each battery?

I have been disappointed in the success of keeping a pack balanced with multiple parallel chargers. Using a slightly larger charger attached to all the batteries in the pack in parallel has been very successful for me - I even used the rig to start my car in an emergency!

You can see it in action in the photos at:
http://visforvoltage.org/forum/4690-new-pack-wiring-geometry-quothummerquot#comment-27783

and the wiring in my XB-600 is cleaner:
http://i200.photobucket.com/albums/aa122/mf70/XB-600/P6210106.jpg

Even with the best charger, I would not leave it attached to the battery while in storage. SLA's "look after" themselves well if disconnected from any possible drain.

Mark

It seems to me that self-discharge varies by the quality of the SLA battery. My original Wilderness Energy batteries seem to hold up better than the V.I.P. battery (cheap) that I bought on ebay. If I go a couple of weeks without riding (fully charging the batteries at the last ride), the range will be no more than 2/3 of the range if I ride and recharge the day before. The V.I.P. battery seems to have a faster self-discharge rate. I checked voltages after a sluggish final stretch a few months ago: the WE batteries were at 12.0v, and the V.I.P. battery was at 11.5 or 11.6v.