<VV> battery tender

[Vair Chris]

I have two vairs.  For a couple of years, I maintained the batteries using a
Dolirum Battery Tender Junior on each vehicle.  Unfortunately, in a short
time, both of these units died, and I had to get new.  I went to batteries
plus, and they recommended the Noco Genius G1100.  So, I bout two of these.
Almost instantly, it said the battery was bad on my 65 convertible, and then
it went into "standy" mode and won't come out of standby mode no matter how
many times I push the mode button.  The other unit is on my 61 rampside.
I've never had any problems with the battery on this vehicle.  Today I went
out to the garage, and all of the lights on the charger were flashing red
and yellow.  So, I unplugged it, waited a bit, and plugged it back in.  When
I plugged it back in, it said my battery was charged to 25%, but after about
30 minutes, it was back to flashing red and yellow again.  

 

Is it more likely that the batteries on both of my vehicles went bad at the
same time, or is it more likely that the Noco Genius G1100 is a crappy
charger/maintainer?  What do you guys use to keep your batteries fresh when
your cars sit for a bit?