Originally Posted by theaveng
One of the photos says "Battery being charged at 151.7 volts and 157.6 mA, using full wave bridge and Variac. This setup needs more attention than constant current setup." That's not really a trickle charge then, because a trickle charge operates at 1/20 C and can be left on the battery indefinitely.
I'd still say it is a trickle charge ... it is fast enough to charge in a day or two ... but slow enough not to be likely to cause significant damage in a day or two ... keep in mind a trickle charge is a bit different from a maintenance charge.
A maintenance charge can be left on for long term Months without any significant damage.... this is the kind of charge you want to be doing as you say , 'indefinitely'
A trickle charge is one that takes a day or two to charge the battery very slowly... but is a faster rate than the maintenance charger ... using a trickle charge as a maintenance charge will result in more degradation to the cell over the course of a year or so than if you had actually used a maintenance level charge.
C/20 for trickle charge is not a hard rule ... it is a general guide line commonly used... it won't hurt the battery to be charged slower at C/25 or C/30 ... or as in the case of ~156mA , about ~C/40... this logic can be continued down to about C/650 or ~10mA ... around there you might not keep ahead of Self Discharge Rate ... depending on temperature and such... and the slower the rate gets you start to move away from trickle charge and into maintenance charge... but it really isn't a hard line , but more of a shades of gray kind of thing... slowly bit by bit transitioning from trickle to maintenance.