Multiple lead-acid charging

Hi guys:

I'm an ME and have run across an application where I need to charge
multiple lead-acid batteries connected in parallel.   The batteries
will discharge at near their maximum continuous current rate when in
use, but will be used relatively infrequently.  In other words, after
a discharge, they may have many hours, or even days, to recharge
before they're used again, so I don't need an aggressive charge rate.
They will always be charged and discharged together, as if they were
one large high-capacity, high-current battery.

What is the best way to charge multiple batteries (say 10 or so)?  It
would be preferable to me to use off-the-shelf items and I would like
to use ordinary 120V power.  Could I use several individual chargers
in shunt?  Do they already make chargers for such an application?  Can
the batteries be used while they are charging, if necessary?

Thanks for any help you can give me.

Don