With test meters I have not seen the battery tender jr taper down or be as "smart" as other transistor or even transformer (with electronics) chargers. They have changed the design at least once if not twice in the past 20 years so not sure what the latest does.
Then you have the very similar item at harbor freight and rural king for 7.99-9.99.
I thing the best you get in these is a on/off circuit.
Some have a two stage kind of thing that acts one way for awhile for initial charging and then kicks into maintain or float mode still kicking on and off based on voltage I'm pretty sure.
They only put out the 900 mA or 1.3-1.5A or not....all or none.
Smarter chargers ( I think most genius ones do this too) will start with max they can do and taper down less and less to a longer time charging amps then to a very low float and then turn off and back on again as the other ones based on voltage. Some even float based on a timer.
Most batteries are just fine on even a chap or basic tender.....CERTAINLY better than letting the, drain and sitting there for who knows how long completely dead.
BUT some times they do boil too much electrolyte off (but if people checked the ones that can be checked this wouldn't be a big issue) and I don't trust them to do an "equalize" charge to help with sulfation. They hit the voltage mark and in a few minutes cycle off. On my larger one I can push equalize button and it does a low amp 4 hr charge. I do this after charging a weak on up to full.
