Hi all, trickle charging at 1/10th. capacity can go on for as long as you want, usually add 40% to this for a full charge. Best to use a dedicated SLA charger, they are not dear preferably an intelligent one which will give a green light when charging complete.

The dedicated charger does not work on constant current, it taper charges i.e. the applied voltage reduces as the charge on the battery increases its' voltage and progresses until the voltage is about equal to the battery. The current is initially limited but is governed by the increasing voltage of the battery on charge.

There is a major difference in how the capacity is measured between SLA and Nimh batteries. SLA are rated at the 20 hour rate and Nimh's at the 5 hour rate.

This means that an SLA of 5AH (or 5000MAhs) capacity will deliver 5/20 amps for 20 hours this is 1/4 amps (250 mamps) for 20 hours. If you take more current the capacity reduces with heat losses etc.

A NiMh battery of same nominal capacity will give the full capacity over a 5 hour period at 1 amp.The SLA can deliver 1 amp easily but for far less time.

I had a 12 volt SLA battery 3.5 Ah driving a boat and the current was 2.5 amps, (30 watts) nothing got that hot but run time was just about 40 minutes. If you convert to watt minutes you will see that the actual capacity available at the higher current was only half the nominal capacity of 3.5 Ahs.

If a NiMh battery was used of 3.5 Ah capacity I would have expected at least an hour running if not more, but I never did the comparison.

Clearly the NiMh battery is dearer but that is what you are paying for. By the way the cylindrical SLA batteries are rated at the 5 hour rate so cost more as well.

Hope this helps some, sorry if I am suggesting ways to suck eggs to the others.

regards Roy