With so many bikes, I'd like to try and keep all of the batteries charged.

Is there a product or method that could enable me to do this?

Thanks.

Google: multiple bank trickle charger. There are several options.

I've found that the little batteries don't care much for constant charging....  or maybe the "float" chargers I've used are not compatible?  (Even though I have a couple of premium chargers from the name brand "Battery Tender")

Anyway, I seem to get the best battery life by following the Yamaha instructions of simply charging the battery monthly.  I use a 30v 10 amp DC laboratory power supply that allows me to precisely set and limit charging voltage and limit current.  It doesn't take very long to do...  if bikes are stored a long time like they are now I keep the batteries on the bench for convenience and just charge them one at a time every month.  I have one Yuasa battery that is almost 6 years old and still in good condition.... on a constant float trickle charger I don't think any lasted more than two years.  Not sure why...  they didn't run out of water or anything. 

Thanks for the replies.