On Mon, 20 Jul 2009 14:32:37 +0100, alo wrote:

I have a 12V 2.8Ah sealed lead acid battery... and a battery charger
that can be set from 50 mA to 300mA.

What should I set the charger at?

Lead acid batteries are charged by setting the endpoint voltage (13.8V
for a 12V battery). NiCd/NiMH batteries are charged by setting the
charging current.

Sealed Lead Acid (SLA) are slightly different in that they are
charged by setting endpoint voltage but with an additional current
limiter and deliberate small overcharge. This is usually done
automatically by the charger.

It isn't usual for a SLA charger to be adjustable in the way you
describe - are you sure it is a SLA charger and not a NiCd/NiMH one?